The World Computer Chess Championship: Stockholm 1974 0852242859

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THE WORLD COM PUTER CHESS C H A M P IO N S H IP Stockholm 1974

Jean E. Hayes David N . L .L evy

'The Stockholm event is a scientific experiment to sum up the resu lts of 25 years' work for the creation of an artificial in t e l l e c t .. . . The championship will contribute to the development of new methods of solving, by means of computers, complex practical tasks and to the problem of creating an artificial in tellect.' M. Botvinnik former world c h e ss champion

Edinburgh University P r e s s

©

1976 J. E. Hayes & D. N. L. Levy Edinburgh University P r e s s 22 George Square, Edinburgh Printed in Great Britain by Unwin Brothers Limited, Old Woking, Surrey ISBN 0 85224 285 9

Contents P reface

v

1. A Short History of Computer C hess

1

2. The Stockholm Championship

11

3. Concepts and M echanisms of Computer Chess

54

4. G lo ssa ry of C hess and Computer C h ess T erm s

70

5. Notes on the Competing P rogram s

74

6. C h ess Thinking

91

Bibliography

96

Appendix 1. Man Against Machine 1974

98

Appendix 2. Computer C hess Challenge 1978

102

Preface In August 1974 at Stockholm the International Federation for Informa­ tion P r o c e s s in g (IFIP) held the first la r g e - s c a le international ch ess tournament in which all the competitors were computer programs. A s m a l l - s c a l e event of this kind took place in 1967-68, when an A m erican program developed at the M assachusetts Institute of Tech­ nology and Stanford University played a Soviet program running in Moscow. The IFIP tournament lasted four days, compared with four months for the previous match, and the quality of the ch ess was much improved; but one element remained the sam e—the USSR won both tim e s . This book is a record of the Stockholm tournament, and is intended for laymen who play ch ess as well as anyone interested in computer sc ie n c e . The second chapter is devoted to a m ove-by-m ove record of each game with com m entaries on the more interesting ones pro­ vided by David Levy, who acted as Tournament Director. Mr Levy is an International Master, and has wagered that he will not be beaten a c r o s s the board by a computer program before the end of August 1978. D etails of this bet are given in Appendix 2.

Acknowledgments Many people have been helpful to us during the preparation of this book. Thanks are due to B .A lm a si, L .R . Atkin, N. B arricelli, A .B a is le y , D. Beal, A. Bell, V. Berman, M. V.Donskoy, R.Hansen, J. J o s s , P. Kent, M.Newborn, J . Parry, R. Prinsen, I.Ruben, F.Sw artz, D.Slate, W.Toikka, J.Winograd and G. Wolf, who all provided material for chapter 5. Also to G .K is s and J.Kalan for help with translation. H .J .B e r lin e r kindly gave us p erm ission to use his commentary as appendix 1, while H. Svedbark generously provided the photographic plates. C riticism and advice given by D.M ichie and R .R o s s have been invaluable. Thanks are also due to Mrs J.Duckman, Mrs E .F itz ja m e s , Mrs G. Ketchin and Mrs J.M oore for their typing a ssista n ce and to Mrs H. Rutovitz who checked the program notes. Finally we would like to thank all the organizers associated with IFIP who made the tournament p o ssib le.

1. A Short History of Computer Chess The idea of a ch ess-p layin g automaton goes back at least 200 years. Moxon's M a s t e r by Ambrose B ierce p resen ts a fictional example, while a r e a l-life one was provided by Baron Wolfgang von Kempelen's celebrated hoax 'The Automaton Chess P layer'. This machine played good ch ess and nearly always won, but a man was hidden inside. The s e c r e t was kept from 1770 until 1824, when one of the 'directors' (i.e. concealed players) fell upon hard tim e s and sold the story to Magasins P i t to r e s q u e s . Another story is that a fire alarm was ra ised and the automaton bucked and heaved, finally bursting open to reveal the d irec­ tor attempting to escape. Some y e a r s later Charles Babbage produced the first genuine work on mechanical c h e ss when he considered how his analytical engine might play the game (1864). Unfortunately, on this occasion he did not have the s e r v ic e s of Lady Lovelace, the world's first, and possibly best, s c ie n c e writer; her record of his work would have been invaluable. As it was, Babbage convinced him self of the feasibility of the idea and then implemented a much sim pler noughts and c r o s s e s machine. This he planned to demonstrate all over the country on a whirlwind fund-raising tour: ' . . . I imagined that the machine might consist of the figures of two children playing against each other, accompanied by a lamb and a cock. That the child who won the game might clap his hands whilst the cock w as crowing, after which, that the child who was beaten might cry and wring his hands whilst the lamb began bleating . . . . When it became known that an automaton could beat not only children but even papa and mamma at a child's game, it seem ed not unreasonable to expect that every child who heard of it would ask mamma to s e e it . . . . ' He was dissuaded by the fact that the dwarf, General Tom Thumb, had already saturated the market for travelling wonders. All records agree that the American midget (real name Charles Stratton) was charming and witty, with a talent for publicity, while Babbage, in spite of his genius, did not have a s a le s personality. About 1900 a Spaniard, T o rres Quevedo, constructed an actual machine for playing the endgame of king and rook against king, and the ideas it incorporated w ere extrem ely advanced for their time. It is said that the machine, which moved the actual p ieces as well as calculating the m oves, was able to force mate in fifty moves, starting from any p osi­ tion. This, however, is not true, as can be seen from the only readily available reference, Vigneron (1914), who quotes the rules for the machine (table 1). As the reader can verify, they are far from com­ plete. However, P r o fe sso r Donald Michie, who is engaged on a study of ch ess endgames, has recently reconstructed a working strategy from Vigneron's account (Michie 1976). He defines two p ieces as being in the sa m e 'zone' if both are in the 3 left-m ost files or in the 3 right-m ost. His computer simulation shows that the T o rres machine could not have worked (see also N em es 1962) unless the p ie ces w ere set up so that the rank controlled by the white rook 'divided' the two kings (see figure 1): also that the w o r s t -c a s e position required 62 moves to mate.

Jean Hayes

2)

Table 1. Rules for winning the endgame king and rook against king as reported by Vigneron (1914). Le roi noir e s t dans la mem e zone que la tour •

n'est pas dans la mem e zone que la tour et la distance verticale entre le roi noir et la tour est plus grande q'un pas

egale a un p a s. La distance verticale entre le s deux r o is etant plus grande que deux pas

egale a deux pas et le nombre de pas qui m esu re leur distance horizontale est

La tour La tour fuit hori­ descend z o n t a l rnent un pas

Le roi (blanc) descend un pas

impair. La tour fait un pas horizontalement

1

3

4

2

pair. Le roi blanc fait un pas v e r s le roi noir

nul. La tour descend un pas

5

6

The m achine's rules can then be translated in strategic te r m s as follows: Is the rook actually, or potentially, in danger? If so, flee. D oes the rook 'confine' the black king? If not, keep advancing the rook. Is the distance between the two kings sm all enough to begin manoeuv­ ring for the opposition? If not, keep advancing the white king. Has the white king achieved direct opposition? If so, exploit with check. If not: Has distant opposition been achieved? If yes, try for direct opposition. If no, make a waiting move. The interested reader will find that, given the above constraints, these five s tr a te g ie s do indeed map onto T o r r e s ’ rules as quoted by Vigneron. and that they work.

Figure 1. The white rook 'divides’ the two kings and a lso 'confines' the black king by giving him no room to advance on the white king. T o rres' machine cannot achieve mate from this position within the 50move rule.

A Short H istory o f Com puter Chess

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From the end of the nineteenth century until the Second World War the field was sluggish, but during the 1940s the English mathematician A .M . Turing d iscu ssed with various colleagues the idea of making computers play ch ess, and in 1948 he and D. G. Champernowne de­ signed a o n e-m ove analyser, the TUROCHAMP. At the sam e time D. Michie and S. Wylie designed the rival MACHIAVELLI, a lso a onemove analyser, which was d iscu ssed in Maynard Smith and Michie (1961) and in Michie (1966). In 1953 another machine of Turing's design was described, but the quality of its ch ess, according to a colleague, was ’abysm al'. Meanwhile, in 1950 the American mathe­ matician Claude Shannon, who had been thinking independently along s im ila r lines, published a paper on computer c h e s s that remained for at least two decades the most significant single contribution to the field. It form s the b asis of all existing ch e ss programs, and som e of Shannon's most important ideas have still to be implemented. In 1955 at Los Alamos J. K ister and his colleagues (Kister et al. 1957) wrote a program for a 6 x 6 board—the bishops w ere omitted—which was occasionally capable of beating a beginner. It searched all pos­ sib le alternatives for a depth of two m oves for each side (a general description of 'search procedures' is given in chapter 3). Two y ea rs later Bernstein el al. (1958) wrote a program for a full 8 x 8 board, a lso searching to a sim ila r depth. Moves were considered in answer to questions such as 'Is the king in check ?' 'Is any of our material under a tta ck ? ’Is castling p o s s ib le ? ’ ’Can a pawn be m o ved ? ’ ’Can a piece be m o v ed ? ’. The seven best moves were chosen, the seven best rep lies analysed, then the best seven rep lies to these rep lies and so on, to a depth of four ply. This idea, of looking only at s o m e of the possible m oves, had in fact been suggested by Shannon in 1950, but this was the first tim e that anyone had tried to implement it. Most c h e s s program s since then have incorporated this feature, which is usually called ’plausibility analysis'. The machine played like a be­ ginner, and m oves w ere made at intervals of approximately eight minutes. Newell and Simon, now at Carnegie Mellon University, Pittsburgh, started work on ch ess programs in the mid-1950s, with the intention of using the programs as an aid in describing and understanding human thinking. They did not use a numerical s c o r e to describe the virtues or dangers of a c h e ss position, typically used by other c h e ss programs and described later, but used the concept of 'goals', each of which corresponded to som e feature of the c h e ss situation such as king safety, m aterial balance, centre control etc. The goals w ere independ­ ent of one another and could be added or deleted without affecting those remaining. Although based on excellent ideas, the program had little experience and little s u c c e s s . In 1962 A.Kotok, then an undergraduate at the M assachusetts Institute of Technology, wrote a ch ess program for his Bachelor's th esis. Five y ea rs later it formed the basis of the Stanford program that played, against Moscow, the first match ever to take place between two com ­ puter program s. The Soviet Union won two gam es and two were drawn. Because of the historical interest of this event we are in­ cluding the reco rd s of the four gam es (see p p .4 - 5 ) , and it might be mentioned that the final position in game 2 is, in fact, a win for Black. The next m ilestone in the history of computer ch ess was the program MacHACK, developed at MIT by R.Greenblatt and others (1967),

Jean Hayes

4) STANFORD- MOSCOW COMPUTER CHESS MATCH* Game 2

Game 1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37

Moscow White

Stanford Black

P-K4 N-QB3 N-KB3 B-B4 0-0 P-Q3 B-K3 P-KR3 B-Q5 P-KN4 QNPXB B-N5 R -N 1 Q-K2 P-Q4 Q-B4 BXN Q-Q3 Px P B-N3 Q-K3 KR-Q1 P-N5 R-Q3 P xR R -R 1 P-Q4 Px P Px N R-R4 N-K5 P-B4 P -B 5 N-B4 N xN P N-B4 R-R3

P-K4 N-QB3 B-B4 N-B3 0 -0 P-Q3 B-KN5 B-R4 B-Q5 BxN B-N3 R -K 1 R -N 1 K -R 1 K -N 1 N-QR4 QxB P-B3 PxP QR-Q1 P-N3 R-Q3 Q-K2 RxR R -Q 1 Q-Q3 PxP NXB P-QR4 Q-K3 Q -K 1 R-Q3 B-R4 R -Q 1 R -N 1 B-Q8 B-B7

Draw agreed

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

Stanford White

Moscow Black

P-K4 P-K5 N-KB3 B-N5 B-R4 B-N3 N-B3 0 -0 P-Q4 PxB BXN B-QR3 PxP R -K 1 R-K3 Q-K2 Q -K 1 B-N4 B-R3 N-N5 N-K4 NXP B xR P-QR3 R-K5 R-QB5 Q-K4 R -Q 1 R-Q2 R -Q 1 R-Q2 Q-K3 Pxp Q-KN3 RPxQ R-B8ch R-B8 PxP P-B3 R-B8

N-KB3 N-Q4 P-K3 P-QR3 P-QN4 B-N5 N -B 5 B-N2 KBxN N-Q4 B xB P-Q3 Px P N-B3 0 -0 B-B 5 Q-B2 P-QR4 K -R 1 P-R3 KR-Q1 RxN QxB N-K2 N-B3 P-K4 R-R3 P-N 3 P-N4 P-R5 P -B 3 PxP N-K2 QxQ N-Q4 K-R2 P-QN5 Nx P N-Q4

Draw agreed

*In gam es 1 and 2 the Moscow program looked 3 h a lf-m o v es ahead In gam es 3 and 4 the lookahead was increased to 5 h a lf-m o v e s.

A Short H istory o f Computer Chess

Game 3 Moscow White 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Game 4 Stanford Black

P-K4 P-K4 N-KB3 N-QB3 N-QB3 B-B4 NxP Nx N B-Q3 P-Q4 BxP PxN P-B 4 BxNch Px B N-B3 P-K5 N-K5 N-B4 Q-Q3 Q-Q5 N-K3 P -B 5 N-N4 P-KR4 P-KB3 PxN PxNP Rxp R -B 1 R xP P -B 3 RxP Q-Q6 R -B 1 R-N8ch Q xr mate

1

2 3 4 5 6 7 8 9 10 11 12

13 14 15 16 17 18 19 20 21 22

23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41

Stanford White

Moscow Black

P-K4 P-K5 N-KB3 B-N5 B-R4 P-Q4 P-QB4?? K -B l N-QB3 Q-K2 PxP

N-KB3 N-Q4 N-N5 P-QB3 P-Q3 Q-R4 N-B7dbl.ch NXR Q-N5 Pxp B-K3 B x P ch P-QN4 N xB BxP Q-B5ch P-QB4 PxN P-K3 N-B3 R -Q 1 Q-B8ch Q x KP B-Q4 Q-K7 P-N5 BXN QxBch Qx KP P-QR4 N-Q5 Nxp R-Q6 N-K8ch RxQch Q-QN4ch R-QR6 R-R8ch Q-Q4ch R-R6ch Q-B4 mate

Q -Q 1

N-K2 B-B2 QxN N(2)-Q4 K -N 1 Q-Q2 Nxp N-B3 Q-N5 B-Q2 B -K 1 Q-B4 Q-N3 B-B3 B -K 1 PXB K-N2 Q-R4 R-QB1 R-KB1 Q-R3 Q-KN3 RxN K -B 1 R-K2 K-K1 K-Q2 K-K3 K-B4

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Jean Hayes

which attracted widespread attention by finding a deep combination involving a rook sa cr ific e . At the 1968 IFIP meeting held in Edinburgh MacHACK took on all co m ers (human) and was su c c e s s fu l in about 50 per cent of the gam es, a performance that can be contrasted with the beginner's standard manifested by the program s of ten years before. Since then MacHACK has been made an honorary m em ber of the United States C hess Federation, and it a lso won an historic match against Dr Hubert Dreyfus, who had publicly a sse r te d that com puters could not play even amateur ch ess. About this time an important theoretical paper by I. J. Good (1968) was published, but its main ideas have yet to be implemented. However, skill and exp ertise in c h e ss programming was developing fast, and by 1970 there w ere enough program s playing sufficiently good c h e s s for the A ssociation of Computing Machinery (ACM) to stage their first computer ch ess tournament as part of their annual conference. Six program s took part, and the three-round S w iss tournament was won by a program called CHESS 3 .0 , which was written at Northwestern University, Evanston, Illinois. CHESS 3 .0 won all its gam es. Each year thereafter the tournament gained in popularity. In Chicago (1971) and Boston (1972) the number of programs was up to eight, and in 1973, in Atlanta, twelve programs w ere allowed to participate out of an original entry of nineteen (the number of rounds was increased to four). Interest in the tournament has grown to such an extent that it has become a main point of attraction at the ACM annual confer­ en ces. The Northwestern program, undergoing continual development, con­ tinued with an unbroken record of s u c c e s s e s until 1973 when, as CHESS 4. 0, it failed for the first time to s c o r e 100 per cent: it drew in the second round. In the 1974 ACM tournament it was defeated by the Canadian program RIBBIT, and it also cam e second at the IFIP World Championship Tournament to the Soviet program KAISSA (although not meeting it during the tournament). In spite of these recent defeats it is s till one of the world leaders, with the distinction of having beaten (albeit at queen odds) both Senior C h ess Master Charles Kalme, and ex-World Correspondence C hess Champion Hans Berliner. There is an Indian proverb 'Chess is a sea in which a gnat may drink and an elephant may bathe.' Unkind c r itic s might say that this was particularly appropriate for computer c h e s s —elephantine in its pro­ cedures and gnat-like in its perform ances—but one thing i s certain: people like to watch it. With the exception of the world c h e s s cham­ pionships, the average attendance at computer c h e ss tournaments is higher than that at human tournaments; perhaps we go to watch c o m ­ puters play c h e s s as we might go to watch bears riding motor c y c le s . Yet the public is not very well informed about the current state of the art: the resu lts of a recent survey on computer c h e ss are given in table 2, and reveal more optimistic b eliefs about the capacity of com ­ puters to play c h e s s than is justified by resu lts. The following questions w ere put to m em b ers of the lay public at Lon­ don Airport (questions 1-6 w ere answered by 42 people, of whom 31 also answered question 7): 1. Can computers be programmed to play c h e s s ? Only four people out of the sam ple of 42 thought that computers could not be programmed

A Short H istory o f Computer Chess Table 2. COMPUTER CHESS QUESTIONNAIRE: Answers from the public Questions 1-6 w ere answered by 42 m em bers of the public at London Airport. Of the sample, 31 also answered question 7 (a) (b).

Yes 1. Can computers be programmed to play c h e s s ? 2. If so, do computers play: w orse than c h e s s m a ste r s? a s w ell a s c h e s s m a ste rs? better than c h e s s m a ste rs? don't know

No

32

Prob- Prob­ ably ably Don't Y es No Know

4

6

—

—

4

4

—

—

10 3 22 3

3. Will computers ever play as w ell a s c h e s s m a s te r s ?

3

4. Will computers ever play better than c h e s s m a s te r s ?

26

9

4

—

—

9

21

3

2

3

8 4

21 25

1 1

— —

1 1

1

5. Will computers play as well or better: by 1977 20 by 1980 4 by 1983 + 10 never 4 don't know 1 6. Is there a computer program at present in existence which can beat Bobby F isch er? 7. Is the field of computer ch ess (a) worth studying? (n = 31) (b) worth government funding? (n = 31)

to play; three of them said 'Never', and the fourth thought that com­ puter program s would play as w ell as m a sters by 1983, but never con­ sistently better. 2. If so, do computers play w o r s e /a s w ell/b etter than c h e ss m a s te r s ? Twenty-five people thought that computers could, at this moment, play c h e s s as w ell or better than m a ste rs. Most of them volunteered reasons for their answer, and although expressed in different ways, there w ere only two basic justifications: (a) a computer has all the information and only has to look at stored positions. (There are more c h e s s positions than p articles in the observable universe.) (b) P ro ­ gram s are written by grandm asters, and hence must reach their authors' standard of play. (The problem of getting information about complex sk ills from people or books into computers has not been solved.) When the answ ers to question 2 are compared with those to question 5,

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Jean Hayes

a discrepancy e m e r g e s. Twenty-two people were prepared to say that computers play better ch ess than m a sters, while only twenty said (question 5) that computers will play as well or better than m a s te r s by 1977. (A colleague suggested as an explanation that c h e s s m a ste rs might be needled into self-im p rovem en t by their current inferior status.) The two people in question gave 1983 as the date by which computers would play m aster ch ess, and they demonstrated a pheno­ menon which was marked throughout the testing: opinions tend to harden during the p r o c e s s of replying to questionnaires. Even people who were logically consistent in the content of their rep lies might be very hesitant in manner when answering question 1, and quite decided by question 5. A better technique might be to return to the opening questions after finishing the survey, or to randomize the order in which questions are presented. 3 and 4. Will computers ever play as well as c h e s s m a ste r s? Will computers ever play better than c h e ss m a s t e r s ? Four people were prepared to say that while computers might play as w ell as c h e s s m a ste rs, they would never be able to beat them. 5. Will computers play as well or better: by 1977, by 1980, by 1983 +, never, don’t know? If we rem ove the three who thought that computers could never be programmed to play ch ess, we have the optim istic r e ­ sult that 50 per cent of the sample thought m a ste r s would be equalled or surpassed by 1977. 6. Is there a computer program at present in existen ce which can beat Bobby F isch er? Twelve thought there was a program now in existen ce which could, in all likelihood, beat Bobby F isch er. 7. Is the field of computer c h e s s worth studying? Is the field of com ­ puter c h e ss worth Government funding? This was 'tacked on' to the survey after questioning had started, and the sam ple s iz e was only thirty-one. Nine of these thought the field probably worth studying but only five thought it merited tax-payers' money. T h ese five gave the following reasons for their support: (a) computer c h e s s is an inter­ national sport, like football, and we spend freely on football (2 replies); (b) the USSR supports computer c h e s s (1 reply); (c) scientific studies are always worth while (2 rep lies). Those who replied 'no' to either or both parts of question 7 w ere usually fairly vehement—e.g., 'Certainly not!' T h ese were p r e s s e d to think of a possible reason for studying and supporting computer ch ess, even if they didn't believe it. Nine people w ere able to do this and replied as follows: (a) computer c h e s s is an international sport (3 replies);* (b) study of computer c h e s s could improve our understand­ ing of c h e s s (2 replies); (c) study of computer c h e ss could improve our understanding of computers (2 replies); (d) it is important to find ways of filling in le isu r e (1 reply); (e) 'If they can make c h e ss work, they can make anything work' (1 reply).

* In 1968 I. J. Good commented: '£500, 000, 000 are spent on football pools in the United Kingdom in five years, and each pound must c o r r e s ­ pond to s e v e r a l hours of study. Further, hundreds of m illions of manhours are expended in watching the game. The expenditure on c h e s s programming (would) be m icroscopic in com parison.'

A Short H istory o f Computer Chess Although tw enty-seven m em bers of this group played c h e s s , none of them belonged to a c h e s s club, or played ch ess ’serio u sly '. The same questionnaire was later given to m em bers of the Edinburgh City C h ess Club, who very kindly volunteered to help. There were fifteen m em b ers in this sample: their mean time as a ch ess player was 32. 5 y ea r s (range 3-83 y ea rs) and their mean time as Club players was 19.1 y ea rs (range 3-46 years). The resu lts are given a s table 3. Note that they a re more accurately informed about the current state of computer ch ess, and a lso were m ore ready to say they did not know the an sw ers. No one was prepared to say that a program would never reach m aster standard, unlike a sm all proportion of people in the first sam ple. When we come to question 7, they are l e s s unwilling to en­ dorse scien tific study and/or government support for computer ch ess than those in sam ple 1. Those who were against support gave two reason s for their attitude: (a) man is over-m echanised already and (b) we cannot afford c h e ss studies in the present economic c r i s i s . One club mem ber, however, thought that government support would sim ply be a bad thing: 'Let's at least keep the government out of c h e s s !' Those in favour of study and support gave as their reason either that such study would deepen our understanding of computers

Table 3.

COMPUTER CHESS QUESTIONNNAIRE: Answers from Edinburgh City C h ess Club.

Y es

No

Prob- Prob­ ably ably Don't Yes No Know

13

—

—

—

2

3. Will computers ever play as well as c h e s s m a ste r s?

7

1

1

0

6

4. Will computers ever play better than c h e s s m a ste rs?

5

2

1

1

6

—

13

—

—

2

9 3

4 7

— 1

— —

2 4

1. Can computers be programmed to play c h e s s ? 2. If so, do computers play: w orse than c h e s s m a ste r s? a s well a s c h e s s m a ste rs? better than c h e s s m a ste rs? don't know

12 1 0 2

5. Will computers play as well or better: by 1977 1 by 1980 2 by 1983+ 6 don't know 6 6. Is there a computer program at present in existence which can beat Bobby F isch er? 7. Is the field of computer c h e s s (a) worth studying? (b) worth government funding?

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Jean Hayes

10)

(as did two m em bers of sam ple 1), or that it would help us to under­ stand our own thought p r o c e s s e s . Before embarking on the Stockholm event itself, let us put computer ch ess in p ersp ective with the aid of tabulated US C hess Federation ratings, as below: F isch er

2780

Average Grandmaster

2565

Average International M aster

2450

US Master

2200-2400

US Expert

2000-2200

US C lass A

1800-2000

US C lass B

1600-1800

US C lass C Best program

1400-1600 ?

Average amateur

1250

It is extrem ely difficult to a s s e s s the real strength of the strongest c h e ss program s. In the opening and middle game 1600 would be a reasonable a sse ssm e n t, possibly even higher, but in the endgame programs play dreadful c h e s s . How then can we a s s e s s the real strength of c h e ss p rogram s? Against a human rated 1400 or even le s s a program would be likely to lose a level endgame position or one in which it held a sm all advantage. For this reason few m a s te r s think that any rating sy stem gives a true m easu re of the strength of a program. Overall, the strongest program s would probably make no m ore than an even s c o r e in a match against a 1550 player, provided that all gam es were played to a conclusion and not adjudicated.

2. The Stockholm Championship The s u c c e s s of the first four ACM ch ess tournaments prompted the idea of a triennial World Championship competition to be held as part of the IFIP C ongress. This plan was conceived on the final day of the 1973 ACM tournament in Atlanta and its first steps were taken at once in the form of an application for approval and financial support from the A ssociated Federation of Information P ro c e ssin g System s (AFIPS). The biggest problem in the early stages was fund-raising. The cost of preparing for the tournament was relatively sm all, and the biggest item of expenditure was the cost of keeping open telephone lines from Stockholm to Moscow, London and the various computer installations in Scandinavia that were being used by som e of the contestants. From Stockholm to Oslo a line cost £6 per hour, to London £19 and to Moscow £29. Fortunately, the local organ isers were able to arrange for many of the program s to run on machines located in Sweden either free of charge or at a nominal cost. Two of the British programs, BEAL and MASTER, shared a telephone line from London and the third B ritish entry was supported by InterScan Data System s where the program was written. The financial support for the tournament came from AFIPS, IBM, CDC, ITT and the National Science Foundation of Am erica. Some of the NSF money was given sp ecifically as a contribution towards the travelling expenses of three of the American programming team s (CHAOS was supported by Univac), but apart from this the program m ers were not supported from tournament funds. Special arrangements were made for Mr Donskoy, the Soviet representative. There was never any doubt that the main interest in the tournament lay in seeing how the best American program s would fare against the Soviet Union, so when the chief program m er in Moscow cabled that his representative could come to Stockholm only if his expenses were paid it was immediately decided to comply. After all, if exceptions can be made for F isch er in one World Championship why should there not be som e reciprocity in a later one? Donskoy's air fare and hotel expenses were met from IFIP funds but in the future this should not be n ecessa ry —KAISSA'S s u c c e s s in the tournament has assured the Moscow programming team of financial support for the future. One major problem in organising a sm a ll tournament is deciding how to r e s tr ic t en tries. It was felt that four American programs would be an adequate representation, and so the four leading participants at ACM73 w ere invited. Later, when it was discovered that there was considerable interest in computer c h e ss in Canada, RIBBIT was also invited. (RIBBIT had scored 4 1/2 out of 5 in winning the first Canadian Computer Championship in June 1974). Announcements in the computer p r e s s and c h e s s journals brought more than a dozen enquiries from Europe, m ore applications than funds would allow. After a few months, however, so m e of the prospective entries dropped out and in the end only one entry had to be refused. On the basis of gam es submitted by the European program m ers it was felt that this program was probably the weakest. Having an odd number of com petitors is a little unfortunate because of the bye, all the more so in a short event. But by carefully organising

12)

D. N. L. Levy

the Swiss sy stem pairings it is p o ssib le to m in im ize the effect that the bye has on the destiny of the p rizes. The S w iss System The ideal form for a ch ess tournament is an a ll-p la y -a ll competition, but in practice this is often not p o ssib le because of the number of playing s e s s io n s required. The S w iss sy stem allows any number of p layers to participate in a tournament. In every round a player is paired against one with the sam e s c o r e or, if that is not p ossible, with one whose s c o r e is nearly the sam e. An attempt is made to ensure that Blacks and Whites even out as much as p o ssib le for all players and, as far as possible, players are given White and Black in alternate rounds. If there is an odd number of players a bye is given in each round to the player with the lowest score: the bye means a free point but since these gifts are only received by the weakest players they rarely have any bearing on the p r iz e s . No player may meet any opponent more than once during the tournament and no player may have the bye m ore than once. To improve the efficiency of the sy stem the players are all seeded at the beginning of the tournament. In human events the seed in gs can be made on the basis of the players' ratings on a num erical sc a le . In the c a s e of computer tournaments one must rely on whatever resu lts the program s have had in the past together with an im p ression formed by studying som e of their g a m es. (At the time of writing a rating list is being compiled for ch ess program s. It will probably com e into use during 1975.) The pairing system makes use of the seedings in the following way. In the first round seed 1 played 7, 8 played 2, 3 played 9, 10 played 4, 5 played 11, 12 played 6, and seed 13 had the bye. Lots were drawn to determine whether it would be the first or second program in each pairing that would have White. In the second and subsequent rounds a sim ila r approach was used in conjunction with the basic principles of the Sw iss s y ste m as described in the first paragraph. Had the seedings worked out exactly seed 1 would have played seed 2 in the fourth round and they would have been due opposite colours. The tie-breaking s c o r e was based on a bonus for winning quickly (or losing slowly). The number of moves in each game won by the program and half the number of m oves in gam es drawn were added and the number of moves in each game lost was subtracted. The Rules Several modifications of the rules of c h e s s are n e c e ssa r y for computer competitions. As new problem s are discovered at each tournament the rules are continually undergoing change. P o ssib ly the most important rule is the one stating 'If a point is in question, the tournament d irector has the authority to make the final d e c i s i o n . ' Since program s do not yet have the facility to claim a draw by th r e e ­ fold repetition of position, the game is automatically declared drawn when the position has occurred for the third tim e. The rate of play, forty m oves in the first two hours and ten m oves per half-hour

The Stockholm Championship

(13

thereafter, is quite common in human tournaments. But there are a few rules that have been sp ecially designed for computer play: 1. The tournament director has the right to adjudicate a game after five hours of total elapsed tim e. The tournament director will not adjudicate any gam es in the first two rounds u n less absolutely n e c e ssa r y . For the third and fourth rounds, any game involving a program that is in a position to finish in the first three p laces will not be adjudicated unless absolutely n ecessa r y . 2. If a team encounters technical difficulties (machine or program failure) during the cou rse of a game, the tournament director may allow them to stop their clock, for a period not exceeding 30 minutes, in order to r e sto r e their sy s te m . After 30 minutes their clock will be started again. The tournament director may grant a team p erm ission to stop their clock up to five tim es during the course of a game, but the total time for such stoppages may not exceed 30 minutes. In the c a se of communication difficulties (terminals or communication lines), the tournament director will make the final decision on time control lim its and on when to invoke back-up v o ic e -to -v o ic e communica­ tion. If the p ossibility of program or machine breakdown a r is e s , the program operator may take no co rrectiv e action without first contacting the tournament director. 3. There is no manual adjustment of program param eters during the cou rse of a gam e. In the case of failures, the program param eters must be r e se t to their original settings if it is at all p o ssib le. Informa­ tion regarding castling status, en passant status, remaining time on his or his opponent’s clock, etc., may be typed in after a failure. If at any tim e during the course of a game the computer asks for the time remaining on either his or his opponent's clock, this information may be provided. However, the computer must initiate the request for information. The P r iz e s The first prize was a gold medal sp ecially designed for and c o m m is ­ sioned by Mr Robert Maxwell, the well-known British publisher. This medal c a r r ie s a design, shown on the end papers, of a globe on which is superimposed a c h e s s king and a computer teletype. Second and third p rizes were engraved blocks of Swedish crystal.

GAME RECORDS The game record s in this book are given in English D escriptive Notation, where K = king, Q = queen, R = rook, B = bishop, N = knight, P = pawn, and ep indicates an en passant capture. In addition to these abbreviations the following sym bols are used: + » ! ? !!

?? !?

?!

check good move bad move excellent or brilliant move dreadful move or blunder interesting or enterprising move dubious move

D. N. L. L evy

14) ROUND ONE: 5 August 1974 Game

White

Black

Result

M oves

1

TELL

THE OSTRICH

0-1

37

2

KAISSA

FRANTZ

1-0

34

3

PAPA

A16CHS

0-1 (time)

22

CHESS 4 . 0

RIBBIT

1-0 (time)

39

5

FREEDOM

CHAOS

0-1

29

6

MASTER

TECH II

0-1

88

4

•

BEAL had the bye GAME 1

White: TELL Black: THE OSTRICH QP Counter Gambit

1 P-K4 P-K4 2 N-KB3 P-Q4 3 N -B 3 ? 3 N x p and 3 P x p both give White the advantage but TELL knows no openings and so continues with its development. 3 ... P-Q5 4 N-QN5 P-QR3 5 N-R3 BxN Typical computer play, doubling its opponent's pawns even though this means exchanging a bishop for a badly-posted knight. N-QB3 6 PxB N-B3 R-QN1 7 P-Q3 0-0 8 Q-Q3 B-Q2 9 10 R-N3 Better would be 10 B-N4 N xB 11 P x N when White's Q -sid e pawns are not so vulnerable. 10 ... P-QN4 11 N-N5 11 B-N4 was s till best. 11 12 13

... N-B3 P -B 4

P-R3 B-K3

If the rook m oves Black captures on QR6.

13

...

PxPep

The Stockholm Championship

(15

Black can win a pawn by 13. . . N P x P 14 P x P N x P but possibly THE OSTRICH incorrectly a s s e s s e d White’s control of the open QN-file as being sufficient compensation for the pawn. 14

RxBP

N-Q5

1 4 . . . B x P ? lo s e s a piece to 15 Q-B2. 15 16 17 18 19

Q -N 1 B-K3 B-Q2 P -R 3 Px N

P -B 4 N-N5 P -B 4 p xp !

Or 19 P x P Nx N+ 20 P x N (or 21 R xN R xR 22 P x R NxP!) 2 0 . . . N x P ! 21 KxN Q x B + . 19 20 21 22

• •• R-R4 P-N3 R-R5

PxN Q-Q4 Q R -B 1

So that 2 2 . . . Q x p 23 QxQ BxQ can be met by 24 RxKP. 22 23 24 25 26 27 28

••• R-R4 B-R3 Bx B B-K3 R-R5 Px N

BxP P-KR4 Q-K3 Px B N-B4 Nx B P -B 5!

Smashing open the position to expose White's king. 29 30 31 32 33 34 35 36

K-B2 PxP K-K1 K -B 1 P -R 4 P-R3 R-KB5 R -B 8+

KR-Q1 R-Q7+ R-K7+ PxP P-K5 Q-Q3 QxNP

Prolonging the game for one move. 36 37 GAME 2

• • •

Q-N3

White: KAISSA Ruy Lopez 1 2 3 4 5

P-K4 N-KB3 B-N5 P-Q4 Q xP

R xR Q-B7 mate. Black: FRANTZ P-K4 N-QB3 P-Q3 PxP N-K2

Normal in this position is 5 . . . B-Q2 but FRANTZ's opening knowledge extended only as far as its previous move. Although the move played is inferior it has been seen in m aster c h e ss (it was once played by a Soviet Grandmaster). 6

0-0

P -B 3

D. N. L. Levy

16) 7 8 9 10

B-KB4 N-B3 QR-Q1 Q-N4?

B-K3 Q -B l B -B 2

Strong is 10 Q-Q3 and then possibly 11 B -B 4 in order to capitalize on Black's weakness along his KN1-QR7 diagonal. The text move is inexplicable—White's queen is placed on a diagonal that belongs to his opponent. 10 11 12 13

•

•

•

BXN+ Q-R4 Q-R3

P-QR3 NXB P-QN4 P-Q4

If 1 3 . . . P -N 5 ? 14 Q-R4 P x N 15 Q xN+. 14

P-QN4

Forced. If 14 Q -N 3? P x P wins a p iece. 14 15 16

... Q-N2 KR-K1

Bxp PXP

P -B 4 ?

More propitious would have been 1 6 . . . 0-0, putting the king in safety rather than trying to keep both pawns. 17 18

N-K5 BXN

N xN

Now White's p r e ssu r e on the long diagonal g iv es him more than adequate compensation for the pawns.

18 19

... BXB?

BxN

Much better was 19 QxB and if 1 9 . . . 0 -0 20 B x N P R -K l 21 B -R 6 followed by mate while 1 9 .. .R-KN1 (amongst other moves) is refuted by 20 Q -B6+ K -B 1 21 B x B P with an overwhelming position. 19 20 21 22 23 24 25 26 27

•

•

•

P -B 3! Bxp B-Q4 P-N3 Pxp B -B 6 RXR Q-K5

R-KN1 Q-N2 Q-N3+ Q-N3 0-0-0 Pxp R-Q4! BXR Q-B2

The Stockholm Championship 28

R-Q1

Bxp??

E ssen tia l was 2 8 .. . P - B 3 when it is not at all clear that White's attack is sufficiently strong to compensate for the pawn. Now B la ck ’s position c o lla p se s. 29 30

QxKP B-K5

K -N 1 R -K l

The b est chance was 3 0 ... Q-K3. 31

Q-B6

Q-N3

If 3 1 . . . RXB 32 R-Q 8+ K-R2 33 R-QR8 mate. 32 33 34 GAME 3

Qx B P + K -R 1 R-Q7 Q-B4 Q -B6 mate.

White: PAPA Black: A16CHS Irregular Opening

On the evidence of its pre-tournament gam es PAPA was expected to be one of the strongest contestants, but a major error was inad­ vertently introduced during last minute changes that were made to the program. As a result, its standard of play during the champion­ ship was in no way representative of its real strength. A further difficulty faced by the PAPA program m ers was that their program was developed on a CDC 3300 and they had not tested it properly on the Cyber 73 computer. 1 2 3 4 5 6

N-KB3 P-Q4 P-Q5 B -B 4 P -B 3 Q-Q4

N-KB3 N-K5 P-K3 B -N 5+ B-R4 PXP??

Losing a piece. 7 8

QxQP Bxp??

N-QB3

Incredible. 8 9 10 11

... BxB Q x N(K4)+ N-K2 P-K3 P-Q4 B -N 5 + K -B 1

Black is a pawn down and therefore refuses to exchange p ie c e s by 1 1 ... B-Q2 12 B x B+ Q xB. 12 13 14 15 16 17 18 19

Q-QR4 N-Q4 P-KR3 N-Q2 P-R 4 R-QB1 Pxp B-Q7 ??

P-QR3 Q-Q3 P-KR4 P-N4 P -B 3 N-N3 B-N5

White's bishops s e e m to think that they are Kamikaze pilots

(17

D. N. L. Levy

18) 19

20 21 22

G AM E 4 •

•

•

•

Q -Q 1 P -B 3 P-K 4 White

BxB B -N 5 B-Q2 N-B5 lost on time.

White: CHESS 4. 0 Sicilian Defence

1 2 3 4 5 6 7

P -K 4 N-KB3 P -Q 4 Nxp N-QB3 B-K 2 N-N3

Black: R IB B IT

P-Q B4 P-Q 3 Pxp N-KB3 P-Q R 3 P -K 4 N-B3 ?!

Black is now out of his openings book and he deviates fro m the traditional 7 . . . B -K2 (or 7. . .B - K 3 ).

8 9 10 11

0-0 B-KN5 Q-Q2 QR-Q1

B -K 2 B-K3

0-0

Now we see why B lack's 7 .. .N - B 3 was weak. Had the knight been able to go to Q2 W hite's 12 B x N would not be a threat. Now, however, Black is forced to submit to a serious weakening of his K - s id e as the bishop on K2 must protect his QP. 11

12 13 14 15 16 17 18

•

•

•

BXN K -R 1 N-Q5 Q-K3 Q -N 3 + P -K B 3 Q-B2

R -B 1 PXB Q-Q2 B -Q 1 P -B 4 K -R 1 R -KN1 Pxp?

A strategic e r r o r . 18. . . P - B 5 would have stopped W hite's K - s id e play but R IB B IT is m o re concerned with undoubling its K B P s . 19

20

21 22 23 24 25 26 27 28 29 30 31 32 33 34 35

Pxp P -B 4 N-K3 N-QB5 NXB N-B5 Nxp Nxp+ Q -N 3 + QxQ+ NXB R-Q 6 R-Q5 P-B5 R-Q7

R-N 2 Q -K 1 Q-Q2 Q-K2 Qx N R-KN1 R-B2 K-N 2 Q-N3 PxQ NxN N -B 2 R -K B 1 R-B 3

Rxp

P -R 4

P -Q N 3 !

Rxp

The Stockholm Championship Threatening 36 B -B 4, against which Black is completely h elp less. 35 36

... R-R7

R-B3

Simpler is 36 B -B 4 R-B3 37 RXR KxR 38 RXN+ RXR 39 B x R KxB when White wins the pawn ending with great e a se. Of course the text is a lso quite sufficient — White wins another pawn. 36 37 38 39 GAME 5

•

•

•

RXR R -R 6+ R xR P

R-B3 KXR K-N2 Black lost on time

White: FREEDOM Irregular Opening

Black: CHAOS

1 P-Q4 N- KB 3 2 P-QB4 P-K3 3 P -B 5 R estricting the mobility of Black's KB but providing an immediate target for attack. 3 Pxp 4 5 N-QB3 6 P-K3 7 B-N5 8 N-R3? 8 N-B3 is the natural move. •

8 9 Why not c a s tle ? 9 10 11 12 13 14 15 16

•

•

... K - B l?

P -Q 3! Q xP N-B3 B-Q2 B-K2

0-0

P -K 4! Pxp B-Q2 Pxp B xN Nxp PxB B-Q B4?? Q-B3 B-Q5 NXB NxN QxN R-KN1 N -B 6??

•

•

•

Overlooking a neat combination.

17

Rxp+!

K -R 1

If 1 7 . . . KxR 18 B -R 6+ winning the queen.

(19

D .N . L. L e vy

20) 18

K-K2??

Best was 18 B -B 3! when 1 8 . . . QxQ+ 19 RxQ B-Q3 20 R -N 3+ N-K4 21 P -B 4 P-KB3 22 P x N P x P + is not at all clea r, while 1 8 .. Q-QN4 + (or 18. . . Q -B5+) can be met by 19 Q -K 2 ! Nx P+ 20 K -K 1 QxQ+ 21 KxQ and Black is lost ( 2 1 . . . B-Q3 22 R x B P + K -N 1 22 R -N 7+ K -R l 23 R-N 6+ and mates). After 18 B-B3 Black must play 1 8 . . . Nx P+ 19 K-Nl N-B6 20 K -B l N-R7 + drawing. 18 19 20 21 22 23 24 25 26

•

•

•

K -B 1 B -B 3 + K-N2 K -B 1 K-K2 K -B 1 K-K2 K -B l

Q-K5+ KXR P-B 3 N-R5+ Q-N7+ Q-K5+ Q-R8+ Q -B6+

Black knows that he is winning and so refrains from repeating the position with 26. . . Q-R8+ or 26. . . Q -N 7+. His next move is based more on the elimination of these two alternatives than on any logical foundation. 26 27 28

•• RxQ R-Q5 •

QxQ+ B-Q3 Bxp

White lost on time. GAME 6

White: MASTER Black: TECH II King’s Gambit Accepted 1 2 3 4

P-K4 P-KB4 N-KB3 P-K5

P-K4 PXP N -K B 3?! N-Q4

Normal is 4 . . . N -R4. 5 6

N -B 3! QPXN

NXN P-KN4

Typical computer m aterialism —Black's primary consideration is holding on to his extra pawn. Better was 6. . . B -B 4. 7

Q-Q5

Even stronger is 7 P-KR4! 7 8 9

•• B-B4 K-Ql

•

N-B3 Q-K2

If 9 0-0 Q -B 4+ and the exchange of queens leaves Black a sound pawn ahead. 9 10

•

•

•

P-N5

Bxp?

Why? 10 11

•

•

•

Pxp

P xN P -Q 3?

The Stockholm Championship

12 13 14

Pxp R-K1 Q-KR5

Pxp B-K3

Threatening 15 R xB .

14

...

BxB

If 1 4 . . . 0 - 0 - 0 15 B-KN5 P -B 3 16 RxB . 15 RxQ+ BxR 16 P-N 3 B -B 8 ? Better 1 6 ... B-K3. 17 18 19

K-Q2 R-K1 R-K4

B-R3 R-Q1

White could shut Black's QB out of play with 19 P -B 4 .

19 20 21

... B-N5 B-K3 ??

B-B8 N-K4

21 BXB KxB 22 P-KB4 wins the knight. 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37

B-N6 RxN? Q x KP B-B 7 Q-B4 B-N6 P -B 4 B-Q4 K -B 1 K -N 1 RPXP P-R4 K-N2 Q-K4+ Q-Q5+ Q-K4+

37

...

•

•

•

P-R4 R-QB1 PXR R-KN1 R-N4 K-Q2 K-K3 R-B3 P-R3 P-R5 Pxp P -B 3 R-KN3 B-Q3 K-B2 K-K2

B-K4 ??

3 7 . . . K-B2 38 Q-Q5+ K-N2 was quite safe. 38

BxB??

(21

D. N. L. L evy

22)

White can win the pinned bishop by 38 P -B 4 R-N5 39 Q -K 1 and if 3 9 . . . Rx KBP 40 B x B P x B 41 Q x p + . 38 39 40

... QxP+ Q-KB5+

PxB K-Q2 R(B3)-K3

Black has a winning m aterial advantage but su ffers from one of the universal failings of c h e ss program s—the inability to evolve a plan. The Winning technique is to march the black king to safety on the Q -sid e and then to combine the two rooks and the bishop in an assault on the white king. Black might also try to win on the K -side by capturing White's KRP (and maybe the KBP as well) and then advancing his own KRP. What follows however, is a demonstration of a im le s s play. 41 42 43 44 45 46

Q-Q5+ Q-QB5+ Q-K7+ Q-Q8+ Q-QR8+ Q-K8

K-B2 R-B3 ? K-N3 K-R3? K-N3

B elieve it or not White didn't repeat the position with 46 Q-Q8+ because he thought he was winning! After 46 Q-Q8+ K-R2 47 Q-R5+ K -N 1 48 Q-K5+ K -R 1 49 Q-QR5+ R-R3 50 Q-Q8+ K-R2 51 Q-Q4+ R(R3)-N3 White has run out of checks but it is still not easy for Black to win. 46 47 48 49 50 51 52 53 54 55 56 57 58

•

•

•

Q-K3 + Q-K8 Q-K5+ Q-Q5+ Q-Q4 Q-K4+ Q-N4 Q-N3+ Q -B2+ Q-N3+ Q-N4 P -B 3 ?

K-B4 ? K-Q3 K-B2 K-Q2 K-K2 B-K7 R(N3)-K3 K-Q3 K-B4 K-Q3 K-Q2 R-B4

White now begins a totally incorrect strategy, advancing his Q -sid e pawns. P rogram s are normally taught that in the end game pawns become more valuable as they advance up the board but here White's advance m erely weakens the position of his King. Had White continued 58 Q-N7+ K-B3 59 P - B 4 . I doubt that Black would have managed to win. 58 59 60

... Q-B4 + P -B 5+?

K-Q3 R(B4)-K4

Better 60 Q-Q4+ K-B2 61 P -B 4 . 60 61 62

... P -N 4 + Q-B8

Kx P K-Q4 R-QB3

The Stockholm Championship 63 64 65 66 67

68 69 70 71 72 73 74 75 76 77 78 79 80

Q -B 7 + Q -B 6 + Q -Q 8+ Q -Q 4+ Q -N 4 + P-R 5 Q -Q 4+ Q -N 4 + K-B 2 Q -N 3 + Q-B4 Q-B8 Q-Q8+ Q-KB8 Q -Q B 5 + Q-B5 Q -B 4 + Q -Q 4 + ?

K-Q3 R -K 3 K -K4 K-B4 K-B3 K -K4? K-B4 K-B3 K -K4? K-Q4 R -B 5 R -B 2 K-B3 B-B5 K-Q2 K-Q3 R -K4

80 Q x p + would o ffe r good drawing chances. 80 81 82 83 84

•

•

•

Q-KB4 QxP+ Q-Q2 P -B 4

B-Q4 R -B 2! K-Q2 RxBP R (B 6 )-K 6 !

The point. Black threatens to win the queen by 85... R-K7. 85 86

Q -Q 1 K-N3

R -K7+

If 86 K-B 3 R (K 4 )- K 6 + 87 K-Q4 B moves and Black wins. But now there is an immediate coup. 86 87

... P-R6

P-N 4!

Or 87 P x B R (K 4 )- K 6 + etc. 87 88

... Q-Q3

R (K 4 )-K 6 + R x Q mate

ROUND TWO: 6 August 1974

White (Score)

Black (Score)

Result

Moves

7

THE OSTRICH (1)

BEAL

1-0

17

8

TECH II (1)

KAISSA (1)

0-1

33

9

CHAOS (1)

CHESS 4 .0 (1) 1-0

79

10

A16CHS (1)

MASTER

0-1

30

11

FRANTZ

PAPA

1-0 (tim e)

30

12

R IB B IT

(0) 1-0 (tim e)

26

Game

TELL

(0) (0)

(0) had the bye

(1)

(0)

FREEDOM

(0)

(23

D .N . L. L e vy

24) GAME 7

White: THE OSTRICH Irregular Opening 1 2 3 4 5 6 7 8 9 10

N-KB3 P-Q4 P-Q5 N-B3 P-QR3 P-K4 B-KN5 P-QN4 B-N5 BXN(B3)

Black: BEAL

N-KB3 N-B3 N-QN5 P-Q3 N-R3 P-K4 N-B4 N(B4)-Q2 B-K2 PxB?

The BEAL program awards a bonus to pawns that capture towards the centre.

11 12

0-0 Q-Q3

0-0 K-N2?

To in crease the mobility of the KR. 13 14 15

N-KR4 P -B 4 N -B 5+

R -K l P-QB4 K-N3

1 5 . . . K -R l would reduce the scope of the KR but the text has an even greater disadvantage—it leads to immediate d isa ste r . 16 17 GAME 8

Q-N3+ K-R4 B-K2 mate.

White: TECH II Black: KAISSA Scandinavian Defence 1 2 3 4 5 6 7 8 9

P-K4 Pxp B -N 5+ B-B4 P-KB3 N-B3 N-K4 N xN + Q-K2

P-Q4 N-KB3 B-Q2 B-N5 B -B l QN-Q2 N-K4 KPxN Q-K2

Better is 9 . . . B-K2. 10 11 12

B -N 5+ Pxp B-R4

P -B 3 Pxp B-R3!

A neat way to develop the bishop. If now 13 Q xB ?? N-Q6++ and 1 4 . . . Q-K8 mate. 13

Q-K4 ??

If 13 P-Q 3?? Q -N 5+,but correct was 13 Q-K3. Now Black can win at once by driving White's queen from the K-file: 1 3 .. . P -B 4 ! 14 Q-K3 P -B 5 15 Q-K4 P -B 4 and 1 6 . . . N -Q 6+ + etc. This variation is more than five ply deep and beyond five ply KAISSA analyses only som e of the forcing variations.

The Stockholm Championship 13 14 15

... N -K 2 KXB

0 -0 -0 ? BxN

If 15 Q x B Q -B 4 ! preventing White fro m castling. 15 16 17 18 19

20

•

•

•

P-Q 3 B-K3 P -B 3 ? B-QB2 Q-QN4

Q-Q2 R -K 1 B-Q3 B -N 1 N-N3

If 20 Q-Q4 Q x Q 21 P x Q B -B 5 winning a piece.

20

...

N-B5+

2 0 . . . B -B 5 also wins. 21 22 23 24 25 26 27 28 29

K-B2 K XR K-K2 PxN QR-QN1 K -B l P-Q 4 K -N 1 K -B 1

RXB! N -Q 4 + Nx Q

Q-Q5 R-K1 + Q-K6 Q -K 7 + QxB

If 29 R -KB1 R -K 7 etc. 29 30 31 32

•

•

•

K-B2 K -B 1 K -N 1

QxR+

Qx N P + Q -K 7 + Q -Q 8+

Why not take the mate in one? The reason is that Black sees m ore than one way to win by fo r c e but he is unable to discrim inate between them (all the winning variations have the same s co re associated with them). The p rogram is th erefore just as likely to take a mate in two as a mate in one. A m ore drastic effect of this tendency is seen in game 9 (note to White's 65th move). 33 GAM E 9

K-B 2

R -K 7 mate.

White: CHAOS Black: CHESS 4 .0 Queen's Gambit Accepted. 1 2

P -Q 4 P-Q B 4

P-Q4 PxP

(25

D. N. L. L evy

26) 3 4 5 6 7 8 9 10 11 12 13

N-KB3 P-K3 Bxp Q-K2 0 -0 B-N3 R -Q 1 N-B3 P-K4 NxQP P-N3

N-KB3 P-K3 P -B 4 P-QR3 P-QN4 B-N2 QN-Q2 B-Q3 PxP Q -N 1

So far both program s have been following their resp ective openings 'books’ but now CHESS 4. 0 is out of its book and must think for itself. 13

...

P-N5

Now CHAOS is also out of its book. 14

N-R4

BxKP

A lso p o ssib le is 1 4 . . . 0-0. The move played is m ore interesting but involves greater risk s. 15

P -B 3

B-N3 ?

Underestimating the force of the ensuing s a c r ific e . The correct continuation is 1 5 ... P-K4! 16 N-K6 (or 16 P x B P x N 17 R x P 0 -0 and Black is better) 1 6 . . . P x N 17 P x B B -B 4 + 18 N xB N xN 19 Q-B4 Q-N4 when White has no attack and Black is a pawn ahead. This variation is given in Neishtadt's monograph on the Queen's Gambit Accepted but no mention is made of any move other than 1 5 . . . P-K 4. CHAOS now lays bare the inadequacies of Black's innovation.

16

N x P !!

A winning s a c r ific e . The CHAOS program could not have calculated as far as move 24 so the s a c r ific e was based on purely positional considerations. As far as I know this is the first example of a positional s a c r ific e being made by a computer program. CHAOS had analysed only as far as 1 6 . . . P x N 17 Q xK P+ B-K2 when it had originally intended to play 18 B-K3, a s s e s s in g the position as equal. It was not until CHAOS played 17 Q xK P+ that it decided to play 18 R -K l Q -Q 1 19 B-KB4 rather than 18 B-K3. 16

...

P xN

The Stockholm Championship 17 18 19

QXKP+ R -K l B-KB4

B-K2 Q -Q 1

Threatening 20 B -B 7 Q xB 21 QxB mate. 19 20 21

... QR-Q1 R-QB1

K -B l R-R2

21 B-Q6 N-KN1 22 N-B5 is immediately d ecisive, e.g. 2 2 . . . NxN 23 B x B + QxB 24 Q -B 8+ etc. The text move, threatening 22 R-B8!, can hardly be bad. 21 22

... N-KN1 R(B1)-Q1 P-QR4

Nothing can save Black. 23 24 25 26 27

B-Q6 QxB(Q6)+ N-B5 P-N 4 B-R4

B xB N-K2 B -B 4 Q -K 1

There is no need to take the bishop yet. 27 28 29 30 31 32

•

•

•

PxB BxN RxQ NxR K-B2

P-N6 PxP P -R 8=Q R-R3 Q-Q l

Why? 32

•

33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53

Q-K6+ Q xN+ RxQ N-B5 Rxp K-N3 PXP R-R6 R-K6+ R-K5 R-N5 B-K6+ P-R4 RxR R-KN5 K-N4 R-QB5 K-N5 R-R5 P -B 4 R -R 1

•

•

K-B2

Why not? K -B l QxQ KxR R-QN1 Rxp+ P-N3 PXP R-QB7 K -B l R-B8 K-B2 K-B3 Rx N KxB K-B3 K-B2 K-K3 K-Q3 K-B3 K-N3 K-B4

(27

D. N. L. L evy

28) 54 55 56 57 58 59 60 61 62 63 64 65

R -Q 1 KxP R-Q8 R-QB8 P-R 5 R -B l P-R 6 R-QN1 P -B 5 R-N8 P -B 6 R-N7

K-N5 K-B6 K-N5 K-N4 K-N3 K-N4 K-R5 K-R6 K-R7 K-R6 K-R5

The reader may wonder why CHAOS does not promote a pawn at once and force mate in three (65 P -B 7 K-R5 66 P -B 8 = Q K-R4 67 Q-R3 mate). The reason is that White has a plethora of continua­ tions that force mate within a sm a ll number of m oves and CHAOS ch ooses between them at random each time it is its move. But since CHAOS knows that threefold repetition of position resu lts in a draw, the program must eventually push a pawn to the eighth rank. 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 GAME 10

K-R4 R-N8 K-R5 R -N 1 K-R6 R-N7 K-R5 R-N8 K-R4 K-N7 K-R5 R-N7 K-R4 R-N2 K-R5 R-N8 K-R4 K-N8 K-R5 P-R 7 K-R4 P-R 8=Q K-R5 Q-R4+ K-R4 Q-QN4+ K-R3 Q-QR4 mate. •

•

•

White: A16CHS Sicilian Defence 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

P-K4 N-KB3 P-K5 P -B 4 P-Q4 P-K N4? Nxp N-B5 kxq

PxB B-Q3 ?? K-Q2 R -Q 1 K-K2 B-K3 ?? Bxp

Black: MASTER P-QB4 N-KB3 N-Q4 N-B2 PxP P-Q3 PxP QxQ+ B xN N-B3 0 -0 -0 N-N5 RXB+ RXR

R-R8 N-B7

The Stockholm Championship 17 18 19

20 21 22 23 24 25 26 27 28 29 30 GAM E 11

NxR P -K 3 N-B7 Nx N Pxp N x RP Bxp R-Q1 + N -B 5 + RxP R -N 5 + R -Q 6 + R-Q R 6 R -R 6 mate.

White: F R A N T Z Black: P A P A Irre g u la r Opening 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

G AM E 12

N-B3 P -N 4 P -Q R 3 N-N5 PxN P -K R 4 P-N 6 K-Q3 K-K3 K-B3 K-N3 K-R3 K -R 2 K -R 1

P-Q 4 P-K4 P -B 3 P -B 3 N-K 2 N-Q2 P -N 3 NXB R-KN1 Rxp B-B4 Q-K2 B-N3 P -Q 5 P -K B 4 PXN PXN Q-B2 KxQ PxP K-N3 Bxp B-N4 K-N2 B -K 6 B -N 8 Bxp K-B2 N-B3 Kx R

White: R IB B IT P e t r o ff Defence 1 2 3

P -K 4 N-KB3 Nxp

P -K 3 B -N 5+? B -B 1 B-Q3 P -K B 4 Q -R 5 + Bxp+ P-B5 PxN N-QB3 P-Q R3 P-Q N4 N-B3 N-K4 N-R4 Nx R QxNP+ QxQ+ B-N2 R -K B 1 + PxP R -Q 1 R -Q 6 + R-B 5 B-B3 R-B4 R -N 4 + P -N 5 R -N 6 ?? Black lost on time. Black: FREEDOM P -K 4 N-KB3 NxP ?

A lrea d y Black is lost! 3. . . P -Q 3 is normal. 4

Q -K 2

P-Q 4

(29

D. N. L. L e vy Q-K2 5 QxN P-Q3 6 P-Q4 and White stays a sound pawn 5

P-Q3

B -Q N 5+?

On 5 . . .Q -K 2 6 P x N Q xN 7 P x p White exchanges queens and rem ains a pawn ahead. The text however, lo s e s a whole p iece. 6 7 8 9 10 11

P -B 3 N-B3 Px N PxP P-Q5 B-Q2

B-Q3 N-B3 P-Q5 0-0 N -R 4? P -Q B 3??

1 1 . . . P-QN3 would save the knight. 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

P-QN4 R -K 1 PxP PxN B-K2 P-K5 P-QN3 Q-N5 Px P Px P N-B3 B-R3 QxQP Bx B KRx Q QxQ Rx B R-Q6 R-QN1 B-B4 K-K2 R(Q6)-Q1 B-K3 R-R6 R-N3 R-R4 BxB PXB R(B1)-QN1 Black lost on tim e.

ROUND THREE: 7 August 1974 Game

White

Black

Result

Moves

13

KAISSA (2)

CHAOS (2)

1-0

36

14

CHESS 4. 0 (1)

THE OSTRICH (2)

1-0

48

15

BEAL (1)

A16CHS (1)

1-0

24

16

FRANTZ (1)

TECH II (1)

0-1

30

17

MASTER (1)

TELL (1)

1-0

27

18

PAPA (0)

RIBBIT (1)

0-1

46*

FREEDOM (0) had the bye GAME 13

White: KAISSA Black: CHAOS Sicilian Defence 1 2 3 4 5

P-K4 N-KB3 P -B 3 PxP P-Q4

P-QB4 N-QB3 P-Q4 QxP B-N5

* Estimated length of game: s e e note at move 31

The Stockholm Championship 6 7 8 9

B-K2 0 -0 B-K3 BxP

P-K3 N-B3 PxP

9 P x p is more natural. White could then continue with N-B3 with an active gam e. 9

...

P-K4

More solid would have been 9 . . . B-K2. 10 11

P-KR3 PxB

Px B B -Q 3! ?

With this move Black launches a dangerous-looking attack. He could have played the conservative 1 1 . . . P x P , forcing the exchange of queens. 12 13

Pxp N-B3

NxNP Q-KR4

Threatening to draw by 1 4 .. .B - R 7 + 15 K -R 1 B -N 6+ 16 K -N l B -R 7+ etc., and if White is c a r e le s s Black may have more. 14

P-KN3

K-Q2 ??

After 1 4 . . . 0 - 0 - 0 or 14. . . 0 -0 it is anyone’s game. The text move is inexplicable from a program of CHAOS* strength. It was made, the CHAOS program m ers discovered later, because of a doubleedged heuristic that encourages the king into an area to which many of its own p ie c e s can quickly move. In general this heuristic worked well, but it so m e tim es discouraged castling.

15

N-KR4

Even stronger is 15 P-Q5! at once, forcing the QB3 knight to retreat ( 1 5 ... N(B3)-K4 lo s e s immediately to 16 N xN + and 17 BXN+). 15 16 17 18 19 20 The best chance.

•

•

•

P-Q5 Q-B2 B-Q3 QxN N-N5

P-B 4 N(B3)-K4 KR-KB1 Nx B QR-K1 P -B 5!

(31

D .N . L. Levy

32) 21

22 23

NXB Q -R 3 + QxP

KxN K-B2 Q-B2

2 3 . . . P x p 24 Q R -B 1 + is no better fo r Black. 24

KR-B1 +

It is slightly m ore accurate to check with the other rook. 24 25 26

... Q-B5+ P-Q 6+

27

R -K1 +

K-Q3 K -K4 K-K3

Instead of typing in this move one of the CHAOS p r o g r a m m e r s input 27 R - B 1 by mistake. F o r a while no-one noticed the e r r o r and the game continued: (27 R - B 1) K-Q2 28 Q-B7 mate. Of course this move is not mate when White's rook is on KB1 but everyon e in the tourna­ ment hall thought that the rook was on K 1. The Soviet re p res en ta ­ tive M r Mikhail Donskoy, confident that the game was over, said goodbye to his colleague in M oscow and replaced the telephone r e c e i v e r . A few seconds later CHAOS printed out the move 2 8 . . . K -K 3! Under such circumstances the usual procedure is to return to the position where the typographical e r r o r was made and resume the game with the c o r r e c t move. In this case the fir s t requirem ent was to re-open the telephone line to M oscow but on enquiring at the Stockholm exchange it was d isco vered that this would take a few hours. Obviously it was v e r y important to finish this game in the proper manner b efore the last round began but M r Donskoy was not at all certain that he would be able to get the use of his computer b efore 7.30 the following evening (Stockholm tim e) when the final round was due to begin. In case it proved im possible to play the gam e out, the following d e c i­ sion was made. The game would be adjudicated a win for White, and in o rd e r to get an estimate of the number of moves needed to win M r Donskoy and I played in consultation against the CHAOS p rogram , trying to predict the moves that KAISSA would make and d elib erately avoiding the best move in some positions. The gam e ended: (27 R - K 1 + ) N -K 6 28 P x P Q-Q2 29 R x N + K-B3 30 R (R 1 )-K 1 Q - N 5 + 31 N -N 2 R-QR1 32 Q - K 5 + K-N3 33 R -R3 P - R 4 34 R x Q + p x R 35 Q -K N 5 + K -R 2 36 R -K 7 R -B 2 37 R x R K - R l 38 Q x p mate.

The Stockholm Championship

(33

The next morning however, Mr Donskoy was able to telephone to Moscow and the resumption of the game was set for 5 p . m . Stockholm time. 27 28 29 30 31 32 33 34 35 36 GAME 14

N-K6 PxP Q-Q2 P -B 5 + ! K-B3 R xN R -Q 1 R-K7 Q-R5 Q-K5+ K-N4 N -B 3 + K-N5 RXKNP+ K-R4 Q-R2+ Q-R5 QxQ mate •

•

•

•

White: CHESS 4. 0 French Defence 1 2 3 4 5

P-K4 P-Q4 N-QB3 Nxp B-KB4

Black: THE OSTRICH

P-K3 P-Q4 PxP B-K2 P -K B 4?

Antipositional. There was nothing wrong with 5 . . . N-KB3. 6

N -B 5?

White should retreat the knight in order to avoid the possibility mentioned in the next note. 6

...

P-B 3 ?

After 6 . . . B x N 7 P x B QxQ+ 8 RxQ P-B 3, Black has a satisfactory position. 7

B-K5

B xN ??

Too late. 7 . . . B-B 3 was n ecessa ry , or possibly 7 . . . N-B3. 8 9 10 11

Bxp QxB Bx Q Bx N

Bxp QxQ N-B3

White has an easy win. The r e s t of the game is of no interest. 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

0-0 P-N4 B -B 3 P-QR4 0-0-0 P -N 5 B-K2 N-Q2 B-K5 NxB N-B3 P -B 4 NxN BxN N-Q7 R -B2 RXB R(R1)-Q1 P-KB5 KXR RXR R-Q7 + K -B 1 RxP R -K 1 R-QB7 P -B 5 RxP P-K4 •

•

•

D . N . L. Levy

34) 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 GAME 15

R -B 5

Rxp R-QN5

P -K 5 R -K 2 P-K 6

PxP

Rx P Rxp+

R -B 2

RXR+

Kx R

K-K3 K-Q4 P-B 8=Q BxQ K-Q3 K-Q2 P -N 4 P -K R 4 K-B2 K-K4 K-Q2 P-R4 K-K2 K-B3 P-Q N 5 P-N6 K -K 2 P-N7 K-Q2 K-B3 P-N 8=Q K-Q2 P -Q R 5 K-B3 P-R 6 K-B4 P-R7 P - R 8 = N ! K-B3 Q-B7 mate K-Q2 P -K N 4 K-K3

White: B E A L Black: A16CHS Irr e g u la r Opening

1 2 3 4 5

6

P-KN3 B-R3 B-N2 P-Q B3 K -B l B-B3

P -K N 3 P-Q B4 Q-N3 Q-B2 B-N2 P -K N 4

A normal move fo r A16CHS: see game 10 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

P-K4 P-Q4 BxP PxP B-K3 N-B3 N-K2 K -K 1 N-Q5 N (K 2)-B 3 N -N 5 Q-Q3 N(N5)-B7 R-QB1 P -K 5

N-QB3 PxP P -Q 3 P -K R 3 Q-N3 Q -R3+ B -R6+ P -N 4 Q-R4 + P -N 5 K -B 1 P-R3 R-QR2 B-Q2 P - B 3 ??

21... P - K 3 wins a knight. 22

P-K 6

N -N 1

The Stockholm Championship If 2 2 ...B -K 1 23 N x B Kx N 24 RxN. 23 24

Q-N6 Q-R5 Q-B7 mate.

A horrible game. GAME 16

White: FRANTZ Queen's Pawn 1 2 3 4 5 6 7 8 9 10 11 12 13 14

P-Q4 N-KB3 B-B4 N -B 3 N-QN5 P-K3 B-Q3 P -B 3 Qx B N-K5 PxN N x RP PxN Q-N5 +

Black: TECH II P-Q4 N-KB3 N -B 3 B-B 4 R -B 1 P-K3 B-QN5+ BxB B-K2 N xN N-R4 NxB R -R 1

Dangerous. 14 N-N5 keeps the extra pawn without incurring any risk. 14 15 16 17 18

•

•

•

QXNP Q-B6 Q-R4 N-B6 ??

K--B1 R- QN1 R--N3 RxP

Now the knight is lost. White should have played 18 0-0 followed by QR-N1. 18 19

... R-Q 1

Q-K1

If 19 P -B 4 R - N 5 ! 20 Q-R6 R-N3. 19 20 21 22 23 24 25 26 27 28

•

•

•

P -B 4 PxP Q-R7 K-K2 K -B 1 K -N 1 Q -R 8+ Q-KB8+ P -N 3

R-N3 RxN PxP B-N5 + R-B7 + Q-N4 + Q-B4 K-K2 RxQ R x BP

Mate in three is just as good as mate in one. 29 30

R-Q3 K -B 1

R-Q7 + Q-B8 mate.

(35

D. N. L. Levy

36) GAME 17

White: MASTER Black: TELL Giuoco Piano

1 2 3 4 5 6 7

P-K4 N-QB3 B-B4 P-Q3 PxP B-N5+

P-K4 N-KB3 B-B4 P-B3 P-Q4 P xP K -B l

Better is 7 N-B3 or 7 B-Q2. 7

...

P-KR4 ??

Correct is 7 ... B-R4 8 Q-R4 P-QR3 9 P-Q5 P-QN4 with equal chances. The move played lo s e s a piece. 8

Q-N3 ??

8 P-Q5 followed by 9 Q-R4+ wins the bishop. 8

...

B-N5 ??

8 . . . B-R4! sa v e s the piece. 9 BxP+ 10 BxN 11 Q-Q5 11 P-Q5 still wins.

K -B 1 Rx B

11 12 13 14 15 16 17

... PxB N-B3 PxB R-QN1 B -B 4 K-K2

BxN R -R 1 BXN P-R4 Q -B 1 Q -R6+ N -Q 1

18 19 20

Bxp+!

P xB K-B2

Q xQP+

KR-N1

Threatening 21 Q-KN6+ and 22 Q x N P + .

20 21 22 23 24

... R-QN5 Q -B 7+ R-K5+ Q x NP

R-KN1 P-KN3 K -K 1 N-K3 R-Q1

The Stockholm Championship 25 26 27

R-N3

QxP

K -B 1 Q-K7 mate RXN+

A convincing finish after som e weak opening play. GAME 18

White: PAPA Black: RIBBIT Irregular Opening 1 2 3 4 5 6 7 8 9 10 11

N-KB3 P-Q4 N-K5 PXN P-K4 ?! B-QN5+ BXB+ QXQ 0-0 R-Q1 + B-K3

P-Q4 N-QB3 NXN P-K3 PxP B-Q2 QXB KXQ P-KB4 K-B3 B -B 4 ?

Before making this move Black was a pawn up for nothing. Now he has a bad ending: White's active rook will wreak havoc. 12 13 14 15 16 17 18

Bx B R-Q7 R x BP + R x KNP P-KB4 PxP N-Q2 ?

Kx B N-R3 K-N3 N-N5 P x P ep N x KP

Better 18 K-B2. 18 19 20 21 22 23 24 25 26 27 28 29 30 31

QR-KN1 N -B 4 + ?? N x N R-N6 ?? P x R R -Q 1 R-Q 1 Rx R Rx R N x NP P-QR3 NxP P-QR4 NxP P -B 3 P -B 4 N-Q4 NxP K-B2 P-K4 K-B3 R-Q5 P-R4 N-R4 + K-N3 Rx P K-B2 •

•

•

At this point PA PA ’s program m ers asked for p erm ission to resign from their program. Since the number of m oves played in this game might affect a tie-break fifteen moves were added (my estim ate of the number needed for RIBBIT to win) to the current total. The game was therefore counted as a win for Black in 46 moves.

(37

D. N. L. Levy

38) ROUND FOUR: 8 August 1974 White THE OSTRICH (2)

Black KAISSA (3)

Result 0-1

Moves 67

TECH II (2)

CHESS 4. 0 (2)

0-1

49

21

RIBBIT (2)

MASTER (2)

l - 0 (time)

59

22

CHAOS (2)

BEAL (2)

1-0

42

23

A16CHS (1)

FRANTZ (1)

0-1 (time)

44

24

FREEDOM (1)

TELL (1)

1/2 - 1/2

24

Game 19 20 §

PAPA (0) had the bye GAME 19

White: THE OSTRICH T orre Attack 1 2 3 4 5

N-KB3 P-Q4 B-N5 P-K3 N-B3

Black: KAISSA

P-K3 N-KB3 P-Q4 B-K2 B-N5 ?!

Wasting a tempo by moving the sa m e piece twice in the opening.

6 BxN?! U nnecessarily conceding the advantage of the two bishops. 6 ... B x N + ?! Returning the favour! Black is happy to double White's pawns. 7 8 9 10 11

PxB B-Q3 0-0 Q-Q2 P x P ?!

QxB P -B 4 0 -0 N-B3

Temporarily gaining a pawn but giving h im self tripled isolated pawns, a liability in the endgame.

11 12

... P -B 4 !

Q-K2

Otherwise Black plays 1 2 ...Q x BP and White can never undouble his pawns.

12 ... PxP 13 B x BP QxP 14 Q-Q3 R -Q 1 15 Q-K4 P-QN4 ? Correct was 15... N - Q 5 ! 16 N xn Q xB with advantage to Black be­ cause of White's isolated QBP. 16 B-Q3 P -B 4 ? Probably 16... P-N 3 17 N-K5 B-N2 was best. 17 18

Q-KR4 P-K4

P-K4

Better is 18 P - R 4 ! e.g. 18... P x P 19 B -B 4 + K -R 1 20 N-N5; or 18... P-K5 19 B x NP P x N 20 B x n .

The Stockholm Championship 18 19

... KR-K1

P -B 5 B-N2 ??

I do not understand how KAISSA, with a five-ply basic lookahead, could overlook White’s manoeuvre. 20

N-N5

P-KR3

Allowing 21 Q x R P + would be much w orse than giving up the ex­ change. 21 22 23 24 25 26 27 28 29 30 31 32

N-K6 NxR P -R 4 B-B 4 + QR-Q1 R-QB1 P-Q B 3! RxP

Q-K7 Q-KB7 R-Q3 B-Q5

Q-N3 Rx N P -N 5 K -R 1 N-Q5 B -B 3 PxP B x RP N-B3 Q-B4 N-Q5 B-N4 ?

Black can force a draw by 32... N - K 7 + ! 33 K -B 1 (33 K -R 1 Q x p is a different story to the game continuation because White’s rook is not on the KR-file) 33... B-N4 34 R-Q2 (if 34 Kx N Q -B 7+ or 34 R-KR3 N -B 6 + 35 K -N l NxB) 3 4 ...N -N 6 + 35 K -N 1 N-K7+ etc. 33 34

R-KR3 K -R 1

35

R-Q 1 ??

N-K7 + QxP

Missing a forced win: 35 R x P + !! P x R 36 Q -B 6+ K-R2 37 Q-K7 + K-N3 38 Q-KB7+ K-N4 39 Q-KN7+ K-R4 40 B-B7 + K-R5 41 Q xR P+ K-N5 42 B-K6 mate. This combination was too deep for OSTRICH. N ev erth eless, White is still winning. 35 36 37

... R-QN1 B -K 6!

Q-N3 R-QB1

Naturally not 37 R x B ? ? R-B8 mate. From now on this mate threat is quite useful to Black. 37 38 39

... Q-N6 Q-B5 ??

R -Q 1 Q-N2

(39

D. N. L. Levy

40)

39 R x P + P x R 40 Q x P + Q-R2 41 Q - B 6 + Q -N2 42 Q x R + K -R 2 43 B - B 5 + K -R 3 44 Q-R4 mate would have been a nice finish. 39 B-B5 K - N 1 40 R x p would also have been decisive. 39 40

... R -R4 ??

Q-QB2 m

Still 40 R x p + . 40 41 42

Q-R3 QxN

N-Q5 NxB B-Q6

Now Black is probably winning. 43

R-KN1

B -B5?

Why not take the pawn ? 44

Q-B5

B-K7

T o prevent 45 R-R5. 45 46

R -R 1 Q-N6

P-Q R 4 P-R5

46... P - B 6 ! would also have been strong. 47 48 49 50 51 52

R -K 1 R -R 1 R-QN1 QxQ

R-R3 R-QB1

B-B5 P-R6 Q-Q3 R xQ P -R 7 R-Q5

M ore convincing would have been 52 ... B-Q6 followed by 53 ... B x P and 54 ... B-N8. 53 54

R(R3)-Q B3 RxP R -R 1 R-Q5

Threatening ... P - K 5 - K 6 - K 7 followed by ... R -Q 8+ . 55 56

RxB P -N 3

RxR

White cannot take the pawn because of mate. 56 57

•

•

•

P -B 6

P-R 3

So that now there is no m ore mate on the back rank. 57 58 59 60 61 62 63 64 65

66

67

•

•

•

R -Q 1 R-QB1 P -N 4 K -N 1 K-B2 R -B 8 + Kx P R-B2 K-B4 K-B 5

R-B7 R-Q7 P-K5 P-K6 P-K7 R-Q8 K -R 2 P-K 8=Q R -Q 6+ P-N 4+ R -K B 6 mate.

The Stockholm Championship GAME 20

White: TECH II Sicilian Defence 1 2 3 4 5 6 7 8 9

P-K4 N-KB3 N-B3 P-Q4 NxP B-QB4 0-0 B-K3 N xN?

Black: CHESS 4. 0

P-QB4 N-QB3 N -B 3 PxP P-Q3 P-K3 P-QR3 P-Q4

A strategic mistake, strengthening Black's centre. 9 10 11 12 13 14 15 16

• • •

PxP Q-B3 B-Q3 KR-K1 P-KN3 B-Q4 ?? B x KP

P xN BPxP B-Q3 0-0 Q-B2 B-N2 P-K4

Or 16 B-K3 P-K 5 winning a piece. 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

•

•

•

B -B 5 B-Q3 PxB Q-B4 R x R+ R -N 1 Rx R K-N2 K-B3 K-K2 B-K4 QXB Q-Q3 QxQ P-QR3 P -B 3 K-Q3 P-R 3 P-QR4 P-R 5 P-N4 Kxp P x RP P-R 6 K-Q4 K-B5 P-R7 P-R 8= Q + K-Q5 K-K4 P -B 3

BxB P -N 3 BxN Q x BP KR-K1 Rx R R-K8+ Q x R+ Q-B6 P -Q 5+ N-Q2 BxB N-B3 K-N2 P xQ N-Q4 K-B3 K-K4 P-N4 P-KR4 P-B 4 N-B5+ NxP N-N8 K-B3 NxP+ P -B 5 K-N2 k xq

N-K4 N-B5 K-N2

(41

D. N. L . Levy

42) 48 49

GAM E 21

K-B 3 K-B 3 K -K4 K -K 3 White lost on time.

White: R IB B IT Sicilian Defence

1

P -K 4 P-Q B 3

2 3 4 Better is 4 . . . P 5

PxP

P-Q4 x

Black: M A S T E R P-Q B 4 P-Q 4 QxP N-QB3 ?!

P 5 P x P P -K 4 .

PxP

QXQ+?

A fte r 5 . . . Q x B P 6 B-K3 White has the advantage but the text is even w o rse—Black never r e c o v e r s fro m the loss of the pawn. 6 7

KxQ B-K2

B -N 5 + 0 -0 -0 +

B lack's fifth move was probably prompted by these two checks and the consequent lead in development. Also, W h ite's extra pawn is a doubled pawn and doubled pawns a re penalised in scorin g functions. Herein lie s one of the fundamental problem s of computer chess: how does one construct an evaluation function that adequately weighs the various positional features re la tiv e to each other ? 8

B-Q2

B etter is 8 K - K 1. The pin proves embarassing later.

8 9 10

11 12 13 14 15 16 17 18 19

•

•

•

N-B3

NxB

B x B+ K-K2 P -N 4 N-B3 N-R3 P -R 3 NxN B-K3 QR-Q1

P-K3 B-K2 P -B 4 R-Q4 N(N5)-K4 NxN KR-Q1 P -Q R 3

RxR

RxR

R -K 1

W h y? 19 R - Q 1 was obvious (it f o r c e s the exchange of m a te ria l) and best.

19

...

K-Q2 ??

Blocking the retreat of his rook.

The Stockholm Championship 20

P -N 3 ??

20 P-K B4 would win material as at move 21 but RIBBIT probably could not calculate to the end of the variation (21 P-KB4) B-R5 22 R-QN1 (say) N-Q6 23 P -B 4 NXBP+ 24 B x N R-Q5 or som e such continuation. White, therefore, prevents ...B - R 5 . 20

...

B-B3 ??

Black should move the king off the Q -file. 21

P-KB4

P-QN4

Black s e e s too late that if he m oves the knight he lo s e s his rook to 22 P -B 4 . Bxp 22 P xN Rx R 23 R -Q 1 Kx R 24 B x NP PxP 25 P -B 4 NxP 26 P-K4 27 K-K2 K-K3 28 B-Q2 P-K 5 29 N-K3 B-K4 2 9 . .. P - B 5 30 N - B 1 P -B 6 + 31 K-K3 is hopeless for Black. 30 N-B4 B-Q5 31 P -B 6! P -N 4 ! If 31 ... P-R3 32 B -B 4 P-N4 33 B-K5! 32 BxP B-B 6 33 P -B 7 K-Q2 34 N-N6+ Pretty, but even stronger was 34 B-B 8 B-Q5 35 N-Q6 and White gets a new queen at once. K xP 34 K-N2 35 N-Q5+ N xB K-B2 36 37 N-Q5+ K-B3 K-N4 N-K3 38 KxP Nxp 39 K-K3 K-R6 40 KxP KxP 41 42 K-Q3 K-N6 B-Q2 43 K-R6 K-B4 K-R7 44 P-KR4 45 B-B 3 N-N7 46 P -R 5 N-B5 K-R6 47 NxP K-R7 48 K-N8 49 N-N6 K-B8 50 K-N3 N-B4 K-N8 51 P-R4 52 N-Q3 BxP K-R8 53 54 P-R4 •

•

•

White has a quicker win in 54 B-Q2 K-N8 55 N-N4 K-R8 56 N-B2 + K-N8 57 N-R3+ K-R8 58 B-B 3 mate. But RIBBIT is not calculating that deeply (nine-ply lookahead) and so im proves his position by

(43

D. N. L. L e v y

44) advancing his passed pawn. 54 55 56 57 58 59 GAME 22

K-N8 K-R8 P-R5 K-N8 P-R6 P-R7 K-R8 P -R 8= Q + K-N8 Q-N2 mate. •

•

•

White: CHAOS Kevitz Defence 1 2

P-Q4 P-QB4

Black: BEAL N-KB3 N-B3

Black's scoring function g iv es too much credit for developing p ie c e s and not enough for controlling the centre with pawns. 3

N-QB3

Better 3 P-Q5. 3 4 5 6 7 8 9 10 11 12

•

•

•

P-Q5 P-K3 P-K4 N-B3 P xN B-K3 PXB P-Q 6 QXP

P -K 4! N-Q5 N-B4 N-Q5 N xN + B-B4 BxB 0 -0 PxP Q-N3 ?

With queens on the board White's exposed king might eventually count against him but after this exchange Black's position is riddled with w eak n esses. Correct was 12 ... Q-R4 or 12 ... R -K 1. 13 14 15

Q xQ

R-Q 1 B-K2

P xQ R-R4

15 R-Q6 R-R3 16 P -B 5 would win a pawn.

15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

•

•

•

R-KN1 K-B2 P-N4 N-Q5 P-QR4 P-R3 R-N4 B-Q3 PxP P -B 6 N-K7 + PxP+ P-N8=Q P-N5

R-B4 R-K1 R-K3 R(B4)-B3 P-R4 P-R 5 N-R4 N-N6 P-B4 R-R3 P-K5 K-B1 KxN P xB P-Q4

If 2 9 . . . R - B 2 or 2 9 . . . R - B 4 30 Q-N7+ wins the other rook. 30

PxR

BxR

The Stockhol m Championship Q-N7 + K -K 1 31 Qx R 32 B -B 1 Qx P 33 N-B4 34 Q-R8+ K-K2 NPxP 35 Qx B PxP 36 Qx N 37 Q-K4 + K-B3 38 Q x P(B6)+ K-K4 39 P -B 4 + K-B4 RxP 40 Another example of a program rejecting the quickest mate(s). 40 K-B3 (or K-N3) and 41 P-K4, or 40 R-KN1 (or QN1) and 41 R-N5 w ere four faster alternatives.

GAME 23

40

...

PxR

41 42

K-B3 P-Q7 P-K4 mate.

White: A16CHS Giuoco Piano

Black: FRANTZ

1 P-K4 P-K4 2 N-QB3 N-KB3 B-B4 B-B4 3 4 N-B3 N-B3 P-Q3 5 0 -0 BxB B-K3 6 PxB 7 P-Q3 P-KR4 Q-K2 8 Nx N 9 N-Q5 N -Q 1 P xN 10 11 P-R4 This program s c o r e s a bonus for moving pawns two squares! 11 P-KN3 12 P -B 3 13 P-QN4 14 PXP 15 B-N3 16 17 P-N5 The culmination of B lack’s itself. •

18 19

•

•

B -B 4 Q-N3

P-K B 4! R-B3 P-QR4 ? Pxp B-Q2 R-QR3 ? R-QN3 ? Q -sid e strategy—his rook has trapped B -K 1 Q-Q2

(45

D . N . L . L evy

46) 20

P-Q4 ??

20 P -R 5 would win the rook for bishop and pawn.

20 21 22 23 24 25 26 27 28

•

•

•

R-QN1 KPx P QPxP K-Q2 K-K2 K-B2 QxR P-K6

N-B2 P-B5 Q-N5! Q x NP + Q x BP + Q-K5+ R x N+ QxB QxQRP??

It was unnecessary to give up this piece but B lack's position is so good that he can afford this luxury. 2 8 ... N-K4 was natural and strong but Black was probably concerned about White's dangerouslooking KP and so he s a c r if ic e s his knight for it! 29

PxN+

BxP

Material equilibrium has been restored but White's king is very exposed and his QP and QNP are weak.

30

Q-QN3

If 30 Q-Q3 Q -R 7+ and 31 ... B x P or 31 ... Q x P, but the text is even worse. 30 31 32 33 34 35 36 36 37 38 39 40 41 42 43 44

•

•

•

RxQ R-K 1 ?? R-QB1 R-QN1 R-QR1 R-QR1 P-R5 P-R6 R-R8 + R-R8 R-Q8 R-K8 + R-KB8+ R-QN8 R-N7 +

QxQ BxP BxR RxP P -B 3 P-N4 P-N4 P-N5 P-N3 K-B2 B-B7 K-K3 K-B3 K-K2 R-N6 K-K3

White lost on time. GAME 24

White: FREEDOM Black: TELL Queen's Gambit Accepted 1 2 3 4 5 6 7 8 9 10

P-Q4 P-QB4 N-QB3 P-Q5 P -B 4 P-K4 B-K3 P-K5 P-K6 PxP

P-Q4 PxP N-QB3 N-K4 N-Q2 N-N3 Q-Q3 Q-N5 PxP BxP

The Stockholm Championship If 1 0 . . . Q x P 11 B-Q4 (threatening 12 N-Q5) with good play for the two pawns. 11 12 13

P-KN3 ? R -B 1 Q-K2

Qx P R-Q 1 Q-R6

Why not exchange queens? After all, Black is three pawns ahead. 14 15 16 17 18 19

N -N 1 ?? N-B3 N-B3 B-Q4 QxB Qx P

Q-R4 + B-Q4 N-R5 BxN Rx B NxN

20 21 22 23

Q -B 6+ Q-R8+ Q-B6 + Q-R8 +

R-Q2 R -Q l R-Q2 R -Q l ??

Black should play 2 3 . . . K-B2 24 B x P + P-K3 25 B x P + KxB but TELL does not know about threefold repetition and so it avoids this line because it lo s e s two pawns! 24

Q -B 6+

R-Q2

Drawn by repetition of position. FINAL SCORES At the end of the fourth round KAISSA had scored 4 points; CHESS 4 .0 , RIBBIT and CHAOS had 3 points each; TECH II, THE OSTRICH. MASTER, FRANTZ and BEAL had 2 points each; FREEDOM and TELL had 1 1/2 points each; and A16CHS and PAPA had 1 point each. (Note that the s c o r e s for BEAL, FREEDOM, TELL and PAPA each include one point for having the bye.) CHAOS was placed fourth on the tie-break sco r e while CHESS 4. 0 and RIBBIT played off for second and third p rizes. This game was played immediately following the fourth round, beginning at approxi­ mately 1 a.m. on 9 August. It was agreed in advance that, if un­ finished, the game would be adjudicated at 5 a.m. when the CDC 6600 was needed for routine maintenance.

(47

D . N . L. Levy

48) GAM E 25

White: R IB B IT P e t r o ff Defence

1 2 3 4 5 6 7

P -K 4 N -K B 3

NxP

N -K B 3 P-Q4 B-Q3 Q-K2

Black: CHESS 4.0 P -K 4 N -K B3 P -Q 3 NxP P-Q 4 N-QB3

N orm a l is 7 0-0 B-K2 8 P -B 4. 7

8 9

•

•

•

N-B3 P-Q R 3?

B-KB4 B-QN5 !

A wasted move that gives Black a big initiative. 9 0-0 was essential 9 10 11

... P xB B-N2

Bx N + 0-0

The only way to avoid material loss was 11 B x N P x B 12 N - N 1. 11 12 13 14 15 16 17 18 19

•

•

•

0-0 Q-Q2 QxB K -R 1 KR-K1 Q-N3 RxR P -N 3

R -K 1 N x QBP BxB N -K 7 + Q-B3 N-B5 R x R+ P -Q N4 ??

19 Q x N P at once is also possible. 19

...

N-R 6

K -N 2 Q xNP N -K 5 P xN QxQ B-B3 R-K7 P -K R 4 ?

Q-B4 Q-Q2 N -B 5 + NxN N xQ N-B3 R-QB1

The best chance. 20 21 22 23 24 25 26 27

27 B - R 5 ! N - K 1 28 R-Q7 wins at least a pawn. White now plays the ending v e r y weakly. 27 28 29 30 31 32 33 34 35

... R -K5 B -N 4 + R -K7 B-B3 Pxp B xN+ R -K 5 P -B 4

K -B 1 P -N 3 K-N2 P-Q R 3 P -B 4 RxP KxB P-R3 RxP

The Stockholm Championship 36 37 38 39 40 41 42 43 44 45

Rxp

Rxp

K-N3 R-Q3 R-QB3 P -B 3 P -B 4 ? R-N3 R-QB3 R-B3 R -B l

R-R5 K-K4 P -B 4 K-Q4 K-K5 P-QR4 P-R4 R-B5

Or 45 R-N3 P-R 5 46 R-KB3 R-Q5 and 47 ... R-Q6. 45 46 47 48 49

•

•

R -B 6+

•

K-N2 R-KN1 R-KB1 R-B2

RxP

P-R5 R-K6 P-R6

Adjudicated a win for Black. The final result of the tournament is shown in table 4.

EXHIBITION GAME Everyone in Stockholm had hoped to s e e a clash between CHESS 4 .0 and KAISSA, but after CHESS 4.0 's defeat in the second round the pairing s y ste m prevented this summit meeting. As a gesture of friendship between the strongest American program and the Soviet World Champion, an exhibition game between the two took place on the evening of 9 August. EXHIBITION GAME 1 2 3 4 5 6 7 8

White: CHESS 4. 0 Black: KAISSA Scandinavian Defence

P-K4 PxP P-Q4 N-KB3 B-K2 0-0 R -K 1 N-R4 ?!

P-Q4 N-KB3 NxP P-KN3 B-N2 0-0 B-B4

Better 8 P-QR3 followed by P -B 4. 8

...

P -K 4 ?

It is difficult to understand why Kaissa played this move. 8 ... B-Q2 was natural and best. Now White has a won game. 9 10

Nx B PxP

P xN N-N5

If 1 0 ... B x p 11 B -B 3 N-N5 12 Rx B winning a piece.

11 12 13 14

Q xQ B-KN5 N-R3 P-QB3

RxQ R-Q2 BxP N(N5)-B3

(49

D. N. L. Levy

50) Table 4.

Final result of the W orld Computer Chess Championship.

P ro g ra m

Authors

Institution

KAISSA (USSR) (Seeded 5th)

V. L . A r la z a r o ff G . M . AdelsonVelskii A. R. Bitman M. V. Donskoy

Instititute of Control Science Moscow, USSR

•

Position (s c o r e ) F irst (4 points)

CHESS 4 .0 (USA) L . Atkin K. Gorlen (Seeded 1st) D. Slate

Second Northwestern University, Evanston, (3 points) Illinois, USA

R IB B IT (Canada) R. Crook, G. Calnek R. Hansen, (Seeded 7th) J. P a r r y

U n iversity of W aterloo, Ontario Canada

T h ird (3 points)

CHAOS (USA) (Seeded 4th)

V. Berman, I. Ruben UNIVAC, Blue Bell, F .S w a r tz , W .T o ik k a Pennsylvania, USA J. Winograd

Fourth (3 points)

B E A L (UK) (Seeded 13th)

D. Beal

Queen M ary C ollege London, England

Fifth (2 points)

FRANTZ (Austria) (Seeded 11th)

J. Koenigshafer G. W olf

Rechenzentrum, Graz, Austria

Fifth (2 points)

M A S T E R (U.K.) (Seeded 8th)

J. Birmingham P . Kent

Atlas Computer Lab. Chilton, England

Fifth (2 points)

THE OSTRICH (USA) (Seeded 6th)

G. Arnold M. Newborn

Columbia U niversity New York , USA

Fifth (2 points)

TE C H II (USA) (Seeded 2nd)

A. Baisley R. Gosper S .K u gell

A r t ific ia l Intelligence Fifth Laboratory (2 points) M .I.T ., USA

FREEDOM (Norway) (Seeded 10th)

N. B a r ic e lli

Oslo University Norway

Tenth (1 1/2 points)

TELL (Switzerland) (Seeded 12th)

J.Joss

Eidgenossische Technische Hochschule Zurich, Switzerland

Tenth ( 1 1/2 points)

A16CHS (UK) (Seeded 9th)

R. Prinsen

InterScan Data Systems, Hounslow, England

Twelfth (1 point)

PAPA (Hungary) (Seeded 3rd)

G. Rajna B. A lm a s i

Hungarian Academy of Sciences Budapest, Hungary

Twelfth (1 point)

The Stockholm Championship 15 16 17

N-B 4 B-B3 B-R 6

P -Q R 4 P -B 3

Although White did not retain his extra pawn he still has a big positional advantage. 17 18 19

... QR-Q1

P -R 5 RXR

RxR

K -R 1 ?

BxN P-B 4

NxB P -N 4

A waste of time. 20 21

Or 21 ... B-Q3 22 N x B P x N 23 R x P followed by 24 R x P and White is two pawns up. 22 23 24 25 26 27

P xB

28

K -B 3

PxP

R-KB1 RxP

K-B2 B-B4

P xN R -Q 1 K -N 1 R -Q 8 + N -Q 1 P -B 3

Hereabouts White begins to play without a plan. This is typical of computer p rogram s and one of the fundamental problems of com ­ puter chess. Of course the endgame should be an easy win and there are probably dozens of winning plans. B u t28 29 30 31

... K -K 4 P -Q R 3 B-K3

R -K B 8 + R-QR8 R -K 8 +

31 K-Q4 allows 31 . . . N - K 3 + 32 K x P R - K 5 + 33 K-Q3 R x B winning. White should have brought his king back to KB2, and started on a different track but White seem s obsessed with the idea of keeping his king in the centre. Now Black’ s counterplay develops. 31 32 33 34 35 36 37

• • •

R-B2 R-Q2 R-Q6 K -B 3 B-Q4 B-K3

R-K7 R-K8 N-K3 N-B4 + N-Q6 P -B 4 K-B2

(51

D. N. L. Levy

52) 38 39 40 41 42 43

R-Q7 + R -KN 7+ RxP K-B4 K-K4 P -N 4 ??

K -N 3 KxP N-K4 + N -Q 6 + NxP

How can A m e r ic a 's strongest p rogram make an oversigh t like th is? 43 K-B 3 was c orrect. N-Q8 43 44 P - N5+ K-N 3 R- R6+ K-N2 45 RxB 46 K- Q5 47 K x P(B5) R x P + RxP K- N5 48 •

•

•

Although a piece ahead it is e x tre m e ly difficult (if possible) fo r Black to win because there are few pawns on the board. 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

P -R 4 R -R6 KxBP N-N7 P-R5 P -R 6 K-B 2 R -K N 6 + K -N 1 R-KB6+ R -K N 6 + K-B 2 R -K B 6 + K -K 2 N-R5+ P -R 6 K-N4 P -R 7 R -B 1 N-B6 K-N3 P-R 8=Q RxQ N -K 5 + NxP K-B4 N-B2 R -R6 R -R 7 + K-K3 K-B4 R -R 6 + NxP K-Q4 Adjudicated a draw.

T H E CLOSING C E R E M O N Y The exciting clash between OSTRICH and KAISSA was the d e c is iv e game of the tournament, since a win fo r Ostrich would have put KAISSA down to equal second with CHESS 4.0. R IB B IT and CHAOS. Imm ediately following it there was a small closing ceremony, although of course the p la y -o ff for second place and the Exhibition Game w e re still to come. P r o f e s s o r Ben Mittman, one of the coorganisors, thanked all those who had helped make the event such a great success. He introduced P r o f e s s o r Zemanek. P resid en t of IF I P , who congratulated the p rizew in n ers and presented the two blocks of Swedish crystal to the R IB B IT and CHESS 4. 0 p r o g r a m ­ m e rs who w e re about to p la y -o ff f o r second and third places. P r o ­ fe s s o r Zemanek then introduced M r Robert Maxwell, who had donated the gold medal fo r f ir s t p rize. A fte r presenting the medal to M r Donskoy, M r Maxwell made a short speech: 'Th e result of the fir s t W orld Computer Chess Championship is a v ic to r y fo r the KAISSA p rogram fro m the USSR. T h is p ro g ra m was written by a team that included M r Mikhail Donskoy, 26 y e a rs of

The Stockholm Championship age, a native of Moscow and a graduate of Moscow University where he studied problem s in control science. 'T h e KAISSA p rogram defeated all of its opponents including three of the four A m eric a n entries. This p rogram is th erefore the undis­ puted winner of the tournament and on behalf of myself, the tourna­ ment d irec to r, the local organising com mittee and all those who have made this exciting tournament possible I am pleased to award, fo r the f i r s t time, the Maxwell medal. 'T h e general public in Sweden and throughout the world who have heard or read about this f ir s t international computer tournament, may have been wondering why outstanding individuals in academic life and industry should be devoting their tim e and public resou rces to what may appear to be a rather childish and unproductive past­ time. But the fact is that the pioneering work c a rrie d on by these dedicated few individuals and teams is bound to lead to a better understanding of how human intelligence works and how man can better harness the computer fo r his own and s o c ie ty 's benefit. 'I hope that governments and individuals all o v e r the world will give all possible help to those engaged in this exciting work.'

(53

3. Concepts and Mechanisms of Computer Chess HOW C O M P U T E R S P L A Y CHESS A computer is a high-speed calculating d evice which can store large amounts of information, p erform arithmetic and lo gica l operations on this information and regurgitate the results of the calculations. By using one storage location for each of the sixty-fou r squares on the chess board, and by denoting a white pawn by (say) 1, a black pawn by —1, a white knight by 2, a black knight by —2, etc., it is a sim ple matter to make a computer appear able to re m e m b e r a complete chess p o s i­ tion in te rm s of the pieces, when what it is actually doing is storing sixty-fou r numbers (empty squares are usually denoted by ze ro s ). E v e ry p ro g ra m m er has his own pet way of representing chess positions and moves, and the following is illustrative: White p ieces

4, 2, 3, 5, 6, 3, 2, 4,

White pawns

1,1, 1,1, 1,1, 1,1,

empty squares

0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,

empty squares

0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,

Black pawns

—1 —1 —1 —1 —1 —1 —1 —1

Black pieces

— 4 ,— 2 ,— 3 ,— 6 ,— 5,— 3 ,— 2 ,— 4,

, , , , , , , ,

An extra number can tell us which side has the move, e.g. or —1 (Black).

+1 (White)

For actually calculating the moves , rather than storing positions, the system shown in figure 2 for representing the board is particularly convenient. The squares are numbered from 11 through 1 8 , 21 through 28, and so on, and each square is labelled with a pair of digits, the rank number followed by the file number. Thus, square 34 is that square which lies in the 3rd rank, and the 4th file. If we now in terpret these digit pairs as though they w e re ordinary decim al numbers (taking 34, for example, to mean th irty-fou r) it is possible to use simple rules of arithmetic that enable a computer to calculate the possible m oves in a given position.

7

71 72 73 74 75 76 77 78

6

61 62 63 64 65

5

51 52 53 54 55 56 57 58

4

41 42 43 44 45 46 47 48

67 68

CO

66

00 00

00

rank numbers

81 82 83 84 85 86 87

31 32 33 34 35 36 37 38

2

21 22 23 24 25 26 27 28

1

11 12 13 14 15 16 17 18 1

2

3

4

5

6

7

8

f ile numbers F ig u re 2.

A typical method of defining the squares on a chess board.

Concepts and Mechanisms o f Computer Chess

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Thus, a knight situated on square n attacks the squares n - minus-21, n-minus-19, w-minus-12, «-m in u s -8 , n-plus-12, w-plus-19, and n-plus21. In the arithmetic expressions to the left of figure 3 the italic num­ b ers are all the possible knight's m oves from square 34, which is c i r ­ cled in the diagram. The squares to which the knight can move are boxed.

34 minus 21 is 13

81 82 83 84 85 86 87 88

34 minus 19 is 15

71 72 73 74 75 76 77 78

34 minus 12 is 22

61 62 63 64 65 66 67 68

34 minus

8 is 26

51 52 53 54 55 56 57 58

34 plus

8 is 42

41 42 43 44 45 46 47 48

34 plus

12 is 46

31 32 33

34 plus

19 is 53

21 22 23 24 25 26 27 28

34 plus

21 is 55

11 12 13 14 15 16 17 18

F ig u re 3.

34

35 36 37 38

The knight's m oves possible from a given square.

Being endowed with the ability to 'r e m e m b e r ' positions and to generate all legal m oves from any position, a computer can 'think' ahead, creating fo r its e lf and tem p o rarily storing all possible positions at any desired le v e l of lookahead. In principle a machine could be designed to play perfect chess, as many of the respondents in our computer chess survey believed to be pos­ sible in practice (it isn’ t). Chess is a special case within a class of games that are finite, two-person, zero-sum (what is good for player A is to an exactly equal extent bad for player B) with perfect in fo r­ mation (both sides have full knowledge of the state of the game) and without chance m oves (von Neumann and Morgenstern 1944). An entire game can be mapped onto a network (called a 'graph' in mathematics) which the read er can envisage as a set of buttons ('nodes') joined to­ gether by pieces of string ( 'a r c s ') . The nodes represent board p osi­ tions and the arcs represent moves, as in figure 4 where 'board positions' are sets of heaps of counters in a 2 + 2 + 2 version of the game Nim. Note that a node may have many p red ecesso rs as w e ll as many successors. It can be seen that such a representation turns out to be rather a chaotic structure. T o sim plify the analysis, it is m ore usual to r e p r e ­ sent a game by a particular form of graph known as a 't r e e ', as shown for the same game of Nim in figure 5. Here each node, except the root node, has one and only one pred ecessor but may have many successors. A node no longer stands for a board position but for a 'partial play' (i.e. a position tagged with a history). Each node has a unique path back to the root node, and this path embodies the total history of the game up to the given point. A graph could in principle be constructed to r e p r e ­ sent the game of chess. In contrast to the sixteen nodes of figure 4 this graph would have around 1045 nodes, the estimated number of d is ­ tinct legal board positions, and conversion to tree form would give a tree with about 10120 terminal nodes. Each terminal node would c o r-

5

6

)

respond to a possible game, i.e. a possible sequence of m o ves played according to the rules.

F ig u re 4. A representation of the simple game of 2 + 2 + 2 N im as a directed graph. Starting with three p iles of two counters, the p la ye rs take turns to rem ove one o r m ore counters fro m one pile and the winner is the p layer who takes the last counter. The lo w e r right-hand digit in each box te lls which side has the move, and the other three digits denote the number of counters in the p iles.

T R E E -S E A R C H IN G AND M IN IM A X IN G The tree representation of a chess game is easy to grasp because it corresponds with our own behaviour. When playing a game we look ahead along a 'tre e of p ossib ilities' saying to o u rselves something like 'If I go there then he might go there, or there, and then I might go there: On the other hand if I went there in the first place, he might go t h e r e . . . ' and so on. Figure 6 shows an actual tree of p ossibilities mentally explored by a chess M aster while considering his next move. A computer program goes through an analogous p rocess, ch aracterised by the m o re or less interchangeable term s 's e a rc h ' or 'lookahead'. Although it is as im possible fo r a computer as fo r a human to look ahead at all possibilities, let us now consider some th eoretica l con­ sequences of doing so.

Concepts and Mechanisms o f Computer Chess

F ig u re 5.

(57

The graph of figu re 4 re-drawn as a 'tre e of partial plays'

Jean Hayes

58)

B

W

B

W

B

W

B

W

B

F igu re 6. A M a s t e r 's lookahead tree, fro m an experim ent of de Groot when studying the selection e x e rc is e d by chess M a s te rs considering possible variations. The analysis ranged from a depth of one ply to nine ply, the total number of positions studied being 47. The average number of branches from each node is about 1.5 (without pruning it would be about 25-30). Chess is a finite game and so it eventually terminates, the final positions being represented by term inal nodes in a tr e e . These term inal nodes can be labelled using the rules of the game with the various possible results or 'outcome values'. Chess has three possible outcome values, labelled traditionally from the point of view of the opening player. They are: +1, a win for W h ite ; —1, a win fo r Black; 0, a draw. Starting from these term inal nodes it is possible to 'back-up' the outcome values from the bottom to the top of the tree. Consider a collection of term inal nodes which all have the same p r e -te r m in a l node as parent. We can g iv e this p r e -te r m in a l node a value, according to whether 'our' side or our opponent's side has the move in the c o r r e s ­ ponding position. If we have the move, we label the p r e -t e r m in a l node with the highest of the values of the various dependent nodes: if, on the other hand, our opponent has control we label this p r e - te r m in a l node with the lowest value of the dependent nodes. This p rocess, con­ tinued up the tree, is known as 'm inim axing',because it is based on the assumption that we w ill be trying to m axim ise the outcome value, while our opponent w ill be trying to m in im ise it—and that neither side makes a mistake. The m inim ax p ro cess can be continued until the starting node (the opening board position) is labelled with + 1 , - 1 , o r 0, which is called the 'g a m e -th e o re tic value'. A game tr e e with backedup ga m e-th eo retic values is shown as figure 7, which shows the same game as figu res 4 and 5.

Concepts and Mechanisms o f Computer Chess

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F ig u re 7. The tr e e shown in figure 5 with its outcome values backed up the tree according to the minimax rule. The result of this ultra­ simple game is thus, in principle, a win fo r the opening p layer provided that neither side makes a mistake. The labels W and L stand for win and lose resp ectively.

Thus the result of a chess game, along with other games in the same class, is in one sense a foregone conclusion, given e r r o r - f r e e play. For this reason, von Neumann and M orgenstern (1944) classed chess as ’ t r i v i a l —which shows, as I. J. Good comments (1968) that von Neu­ mann and M orgen stern 's game theory has t r iv ia l relevance for the purposes of p ractical chess. Lasker once called chess ’ stereotyped' and stopped playing for two years, but this was presumably because he lacked sufficiently challenging opposition rather than because he believed he had 'solved ' chess in the von Neumann sense. It is not practically possible to calculate the outcome value of chess, but since we know that there must be such a value, which is computable in principle, it is interesting to speculate what it might be. Some people invoke the number of drawn games in m aster play and suggest that the statistical evidence points to the gam e-th eoretic value being 0; some have suggested that chess must give a forced win for White (+1), citing cases where White has won and commentators have been unable to find Black’ s losing move. No-one as far as we know has e v e r sug­ gested a forced win for B lack! Speculation of this kind is however an academic e x e rc is e . De Groot (1965) observed that there are of the ord er of thirty possible con­ tinuations from any chess position, and that the number remains r e ­ markably constant until nearly the end of the game (see figure 8). An average game lasts, at a conservative estimate, for some forty moves. (This is an understatement in the case of computer chess, which is

Jean Hayes

60)

log 10 (no. of legal m oves)

played to checkmate and not to resignation: games of 60-70 m o v es are frequent.) As rem arked e a r l ie r , there are some 10120 variations to be calculated from the initial position and thus, according to Shannon (1950), a machine would take over 1090 y e a rs to calculate its f ir s t move. The universe is only about 1010 y e a rs old. 1090 y e a rs is not a figure which can be sensibly reduced by making faster machines, fo r a machine playing a thousand tim es faster would s till need 1087 years.

move in game

F ig u re 8. The number of legal m oves fro m a chess position (Shannon 1950, after de Groot). Another possibility, also mentioned by Shannon, in a bid to play perfect chess, would be to store in the machine a 'diction ary' of e v e r y possible position matched with its c o r r e c t subsequent move. Here the number of entries would be about 1045 (one entry for each distinct board p osi­ tion), and a machine with this storage capacity could not fit on the planet. Fu rtherm ore the only way of finding the entries to put in the dictionary would be to do the 1090- y e a r calculations first. These figures have been calculated in different ways by s e v e r a l people and the results are always much the same. However, non-mathe­ maticians tend to regard them with some scepticism , feelin g that there is a catch somewhere. R. L. G re go ry (1970) points out a possible reason for this: 'Th e mathematical notion of physical quantities in­ creasin g by a power law evidently is not w e ll represented in our p e r ­ ceptual models and intuition then fails d ra m a tic a lly'. He then g iv e s the following striking example of our d efective modelling: 'We have all, as children, folded pieces of paper and as adults we fold letters and newspapers e v e r y day. Imagine p e rfo rm in g the following operation and trying to visualise the result. In imagination take a sheet of tissue paper a few thousandths of an inch thick and as la rge as you like. Now fold it in half. Now fold it again so the double thickness becomes four thicknesses. Repeat this folding fifty times. Now how thick is the folded paper? People usually give an answer between 1/2 inch and 3 feet. But the answer is that the thickness of paper would be about the distance of the sun! It seem s quite absurd that all we have to do to reach the sun is to fold a piece of paper fifty tim es and yet this is indeed so.'

Concepts and Mechanisms o f Computer Chess

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The tissue paper would need to be of non-standard size, but the point is w e ll taken! Th is escalation of the number of possibilities (som etim es called 'the com binatorial explosion') helps the rea d er to see that the method of calculating a ga m e-th eo retic value in principle, by backing terminal values up the entire search tree, is not rem o tely adequate for chess. Both Shannon and Turing independently a r riv e d at the idea of a modified procedure, whereby a search tree of a practicable depth could be grown, and each position at this depth is given a numerical score; in e ffec t a guess at its ga m e-th eoretic value based on strategic features of the position. These s c o re s can then be backed-up the game tree in an exactly s im ila r manner to that described e a r li e r . Figure 9 shows this p rocess, highly sim plified, with a tree three 'h a lf-m o v e s ' deep (three ply). (When we speak of the depth of a lookahead it is customary to use the term 'm o v e ' to denote our move together with the opponent's reply, so that the depth is spoken o f as so many 'h a lf-m o v e s ' or 'p ly '.) Four ply is usually regarded as a minimal search depth for playing 'res p e c ta b le ' computer chess, though most p rogram s employ a deeper search. In highly 'fo r c e d ' combinations m oves may be considered as deep as fifteen ply.

F igu re 9. A search tree demonstrating the p ro c e s s of minimaxing with evaluation to a depth of three ply. The positions have been given s co re s that re fle c t their value to the p layer who has the move, and these are backed up the tr e e . T his type of search is term ed 'breadthf ir s t ': all su b-trees are grown, and then evaluated, at the same tim e. Another type of search, 'dep th -first', is described later. To understand figure 9, assume that the game has reached position X, and that 'our' machine has the move. It grow s a search tree of the possible m oves open to it at X (three in number in this example), our opponent's r e p lie s (seven), and our own possible (fourteen) answers to the latter. At this third le v e l (three ply), the machine s co re s each position according to previously determined rules: the higher the score, the better the position from 'our' point of view. Now, starting from the bottom, the machine backs the s c o re s up the tree, using the minimax rule. Thus, at ply 2, where we have the choice of move, each node is given the highest of its offsprings' s c o re s (numbers shown in brackets

62)

Jean Hayes

in the figure): i.e. 30 is the maximum of 5 and 30; 90 is the maximum of 90 and 0, etc. Backing up again, we reach ply 1, where our opponent has the m ove and w ill choose m o v es with the lowest values: i.e. 30 is the minimum of 30, 90 and 35;—10 is the minimum of —10 and 20, and 18 the minimum of 50 and 18. Backing up again to X we have the m ove and can choose the highest of these ply 1 s co res, namely 30, to determ ine our move. This p ro ce ss can be generalised to a search tree of any size. Each time the program is called upon to make a new move, the p ro ce ss of lookahead, evaluation, and minimaxing starts all o ve r again. The ’ s c o r e s ' r e f e r r e d to above are computed by an 'evaluation function' that combines, with different weightings, features such as m aterial ad­ vantage (a conventional scale of m a te ria l values is P = 1, N = B = 3, R = 5, Q = 9), pawn formation, mobility, control of centre, position of pieces (e.g. doubled rooks, advanced knight etc.), attacks, pins, etc. N U M E R IC A L E V A L U A T I O N O F POSITIONS In the section devoted to notes on the competing p rogram s, the re sp e ctive evaluation functions for CHAOS and THE OSTRICH (both A m erica n p r o ­ gra m s) are discussed in some detail. CHAOS uses nineteen features and THE OSTRICH only thirteen, but the latter plans to increase this number in later incarnations. They have approximately eleven features in c o m ­ mon: 'approxim ately', because the concepts are divided d ifferen tly. The overlap is not surprising since all scorin g functions aim to embody 'r e lia b le ' chess heuristics: the weightings may d iffe r, but the features themselves are s im ila r . One of the eleven concepts shared by CHAOS and THE OSTRICH is m aterial: this is the dominant factor not only in these two program s but also in the m a jority of chess playing p ro gram s. Exceptions are FREEDOM, which s tr e s s e s mobility, and P A P A , which concentrates on 'entropy' (basically a m obility m easure). Other shared concepts include mobility, control o f the centre, castling, king safety and assorted term s concerned with pawn structure: the latter include bonus points for occupancy of the centre, advancement, passed pawns, a bonus for doubling opponents' pawns with a penalty for doubling one's own, and a penalty for blocking development of one's own pieces. The delicate matter of handling pawn structures has not been m astered s a tisfa cto rily by any current program , although an interesting th e o reti­ cal analysis by S. T. Tan (1976) of Edinburgh has appeared. F o r in­ stance, all seem to place disproportionate faith in the concept of doubling the opponent's pawns (see re co rd s of games 1 and 4). CHAOS also considers the number of threatened pieces, pins and d isc o ve re d checks, king end-game position, and capturing and m obility potential. THE OSTRICH has an interesting term, concerned with tempi, which aims to penalize tim e-w astin g m oves such as taking two m o ves to reach a square that could be reached in one, or repeating a m ove (see game 24, where the Swiss program T E L L causes a draw by repetition). P r o g r a m s which do not prohibit a longer route to a given state than is s trictly n ecessary can exhibit b iz a r r e behaviour, by human standards. For instance a program may treat mate in one as no better and no w o rse than, say, a forced mate in ten: see gam es 8, 9, 16 and 22. The reason is that most p rogram s give equal weight to each winning v a r i a ­ tion and choose among them at random. W HEN TO E V A L U A T E T h e re is an important concept related to the point at which an evalua­ tion function is applied. C le a rly it is not worth working out a s c o re

Concepts and Mechanisms o f Computer Chess

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half-way through a sequence of exchanges: positions chosen for evalua­ tion should be 'dead' positions (Turing) or 'quiescent' (Shannon). Good has suggested that the latter is the better term, since it is convenient to think in te rm s of d e g re e s and this is v erg in g on the facetious in the case of 'dead'. De Groot, however, is happy to talk of a position being 'r e la t iv e ly dead'. This is one of many reasons for p ro gram s having a variable depth of lookahead. A program may always construct a search of lookahead tree to perhaps four half-m oves, and then look further at, say, captures. A program which always looks exactly n ply deep cannot take account of quiescence (and may o verlook a capture at n + 1). The program CHAOS exists in two versio n s; one has a fixed depth of lookahead, and one a v a ria b le lookahead. It seem s at present that the fo r m e r does better, but this is expected to change when the c r it e r ia on which fu r­ ther search depends have been re vis e d and improved. P r o g r a m s d iffe r from one another in the re la tiv e emphasis given to evaluation versus search. The British program , M AS TE R , is regarded by its authors as fir s t and forem ost an efficient search program : it just happens to be using chess as its problem domain. KAISSA gives m o re attention to c r it e r i a for controlling the search than to the evalua­ tion of positions. The Soviet p ro gra m m er M. V. Donskoy remarked humorously at Stockholm: 'W e have had the same evaluation function for many years: no one knows any longer what is in it'. ’ P R U N IN G ’ TH E T R E E E fficient search is the backbone of current computer chess program s. Since search procedures consume so much time or space, much in­ genuity has been expended on 'pruning’ useless search and cutting out wrong, irre le v a n t or unpromising lines. Forward priming is usually by means of 'plausibility analysis’ ; the concept was put forward by Shannon but the term is due to Samuel (1967). This is a method of ordering m oves at a given position so as to rem ove from further con­ sideration those placed low in the order. A ll legal m oves are initially listed, and each one is given a plausibility score; checks, captures, pawn promotions, etc., would be given high s co res, m oves to attacked squares or to the side of the board would attract penalties. The plausi­ bility analysis used by THE OSTRICH is shown as a flow chart in chapter 5. Plausibility analysis may use some d egree of ’ m in i-look ­ ahead’ in the assessment of some of its c rite ria . The number of m oves examined (i.e. classified as plausible) normally changes at different le v e ls in the search tree. This number is often r e fe r r e d to as ’ fanout’ . T yp ic a l fanout settings in, say, a s ix-p ly search might be; look at the fifteen most plausible m oves at ply 1, the twelve most plausible at ply 2, ten at ply 3, eight at ply 4, six at ply 5 and four at ply 6. The heuristics used in formulating the plausibility analysis may w ell be s im ila r to those used in an evaluation function. It should be r e m e m ­ bered, however, that the f i r s t is concerned with moves and the second with positions, and the s im ila rity of these factors va ries fro m program to program .

Backward pruning is usually c a rrie d out by means of the alpha-beta a l­ gorithm, a method by which a program can discard a bad move without having to search continuations from it to find out just how bad it is (a

Jean Hayes

64)

characterisation of alpha-beta which we owe to A m e ric a n Chess M aster Charles Kalm e). Figure 10 shows a search tree pruned by the alphabeta algorithm, sim plified to 'toy' s ize in o rd er to illustrate the p rin ­ ciple.

evaluation scores

F ig u re 10.

The principle of the alpha-beta cut-off.

The alpha-beta rule can only be undertaken in conjunction with a form of search known as ’ d ep th -first’ . Our expositions so far have fo r con­ venience been based on the 'b re a d th -firs t' style. The distinction is illustrated for the sim ple t r e e of fig u re 10 in figu res 11 and 12, fro m which it is evident that under the 'dep th -first' r e g im e the o r d e r in which the successors of each node are arranged w ill affect the o rd e r in which they are tra v e rs e d in the search and, with alpha-beta pruning, even whether they are tr a v e rs e d at all. Hence the savings which can be derived fro m this technique are dependent on the goodness of the p r io r plausibility ord erin g of the nodes. With optimal ord erin g the e ffe c tiv e depth of search is approximately doubled fo r a constant allocation of computational work. In figu re 10 it can be seen that as soon as the result of move g has been evaluated and found to be le s s than e a r l i e r evaluations, the last two variations h and i need not be considered by the opening players. M o v e g is called a refutation move to move C. The principle can be gen eralized to cope with tr e e s of any magnitude, and a much la r g e r tr e e is shown in fig u re 13 to demonstrate the s i z e ­ able amount by which use of the alpha-beta algorithm can cut down search. As noted above, its efficien cy depends on the p r io r o rd e rin g of the nodes and thus forw ard and backward pruning methods may usefully be used in conjunction. Is is often useful to list and save refutation m oves—this is known as the 'k il le r heuristic’ . A move which is a refutation in one position may also be a refutation in another, and such a move is worth c o n s id e r­ ing e a rly since it may allow the elimination of a number of alternatives which might otherwise waste much time. K NOW LEDGE IN CHESS Current computer p rogram s are directed towards playing a tactically skilful middle game. L ittle attention has been given to the opening, although most p rogram s have stored book openings: in essence an application of Shannon's 'big dictionary' concept. Here the dictionary is limited to the fir s t few m oves and hence its construction is feasible. Computer chess is at its worst in the endgame, which is agreed to be intellectually the deepest part of chess. The Stockholm p ro gram s

Concepts and Mechanisms o f Computer Chess

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F ig u re 11. 'B re a d th -firs t' search, shown in successive stages. Nodes are sprouted le v e l by le v e l. step 1

F igu re 12. 'D ep th -first' search. At each successive stage the p rocess runs as fa r as it can, always turning to the left of the page and never running down the same path tw ice. It backs up to the next higher level whenever forw a rd p r o g r e s s is impossible, and then re -a p p lie s the above r u le .

66)

F ig u re 13.

Jean Hayes

Alpha-beta pruning a la r g e search tr e e (Samuel 1967).

Concepts and Mechanisms o f Computer Chess

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either vary their evaluation function on reaching the endgame or make use of special heuristics. The difficu lties of mechanical endgame play have been considered by Barbara Huberman (1968) and by Soei Tan (1972, 1974, and 1976). Huberman was esp ecially concerned with getting information from books into machines. Indeed, although it is now thought that computer chess re q u ires p ro g ra m m e r s or 'teach ers' of advanced chess ability, there is still no high road to the transfer of the m a s t e r 's perceptions and knowledge into current program s. The A m e ric a n Grandmaster Reshevsky once said: 'Chess fo r me was a natural function like breathing. The m oves in a game occurred to me as spontaneously as I drew breath. If you consider the difficulty that you might have in accounting for that everyday action you w ill have some inkling of my d ilem m a in trying to explain my chess ability.' These problem s are considered further in chapter 6. Table 5 giv es a summary of the program mechanisms used by twelve of the Stockholm program s, and also tabulates some information about machine s iz e and the computer languages used. A glossary of chess and computer term s follows, to assist the reader with any technical descriptions in chapter 5.

Jean Hayes

68) Tab le 5.

Basic information concerning 12 of the p ro g ra m s entered f o r the A16CHS (U.K.)

BEAL (U.K.)

CHAOS (U.S.)

CHESS 4.0 (U.S.)

FRANTZ (Austria)

NO

NO

7500 positions

5000 positions

YES

2. Minimax tree search with evaluat ion function

YES

YES

YES

YES

YES

3. Alpha-beta (or equivalent) cut-off

YES

YES

YES

YES

YES

4. Forward pruning YES by mini-lookahead

YES

YES

NO

YES

5. Special routines for endgames

NO

NO

Different Special heuristic in evaluation function evaluation function

GCS- Alpha 16

CDC 6000

UNIVAC 1110

CDC 6600

UNIVAC 494

(tournament site)

London, England

Bergen, Norway

Stockholm, Sweden

Stockholm, Sweden

7. Language used:

Assembly

FO R TR A N / Assembly

FORTRAN

Assembly

Assembly: o v e r a ll logic in FORTRAN

8. Program size:

11 K (but growing)

20 K words when executing

64 K 36-bit words

150,000 characters

32 K 30-bit words

1 man, 7 months

1 man, 1 year

approx. 5 manye a rs

1. 5 men for 1 man, 5 yrs. O v e r ­ 1 year lap of ideas with CHESS 3 . 5 , none with code

1983 +

by 1978

1983 + (approx. y r . 2000)

1983 + (probably never)

Program information 1. Stored book openings

Machine information 6. (a) Machine used:

(b) Location:

Other information 9. Approx.tim e invested in the program

10. Predicted date at which program will play at International Master le ve l:— 1977,1980, 1983+

YES

1983 +

Concepts and Mechanisms o f Computer Chess

(69

Stockholm Championship. EEDOM rway)

KAISSA (USSR)

MASTER (U.K.)

OSTRICH (U.S.)

RIBBIT (Canada)

TE CH II (U.S.)

10,000 positions

280 lines 10 moves

500 posit ions

2000 positions

2 standard NO openings

S

YES

YES

YES

YES

YES

YES

S

YES

YES

YES

YES

YES

YES

YES

YES

YES

YES

NO

NO

NO

YES

NO

YES

NO

|

TELL (Switzerland)

%

rch depth Special reases as evaluation ernatives function few er

%

C ber 74

System 4/70

IBM 370/195

Data General Honeywell NOVA 840 6060

DEC System 10

ller, rway

Moscow, USSR

Chilton, England

(tournament site)

Vasteras, Scandinavia

Stockholm, (tournament Sweden site)

RTRAN/ sembly

Assembly

PL/1

Assembly

FO R T R A N

Assembly

Assembly

K -bit rds

384 K bytes

150 K bytes

8000 words

23 K 36-bit words

70 K 36-bit words

8 K 16-bit words

nan rox. ears

approx. 5 manyears

Original 25 months written 8 years ago. This v e r ­ sion, 2 men fo r 1 year

approx. 10-12 p ro ­ gram m er months

3 months (but based on TECH)

1 man, 2 years (spare time)

1980+

1983+

1977 (possibly)

1983+

1983+

3

1983+ (1990)

Hewlett Packard 2100

4. Glossary of Chess and Computer Chess Terms CHESS T E R M S 1.

FIDE. Federation Internationale des Echecs: the governing world organisation for chess: which draws up rules of play, organises the w orld championship and awards titles of International Grand­ master, International M aster etc.

2.

Expert. A term used in the USA for p layers rated 2000-2199 on the USCF (E LO ) scale.

3.

National M aster (e.g. A m erican M aster). A title (awarded by in­ dividual national organizations) whose value v a rie s ; Soviet M a s te rs are strongest.

4.

International M a s te r . T itle awarded by FIDE.

5. International Grandmaster. T itle awarded by FIDE. A higher award than International M aster. 6. Opening. The e a rly part of the game in which both sides develop their forces. 7.

Middle game. Follows the opening—when most of the struggle takes place.

8.

Endgame. Follows the middle game, when few p ieces are left on the board. The most difficult part of the game to play, by far.

9.

F o r ced move. A ll alternatives are fatal.

10.

F orced m a te . Mate that cannot be prevented even though it may be s e v e r a l m oves away.

11.

Forced variation. Variation that cannot be prevented even though it may be s e v e r a l m oves long.

12. Opposition. Endgame situation in which the two kings face each other along a rank, file or diagonal with one intervening square. 13. Distant opposition. Endgame situation in which the two kings face each other along a rank, file or diagonal with 3 or 5 intervening squares. 14.

T im e control. The point at which the specified rate of play must have been accomplished otherwise the game is lost on time.

C O M P U T E R AND C O M P U T E R CHESS T E R M S 1. Algorithm . A systematic p ro cess that guarantees to find a solu­ tion to a problem if a solution exists, or to recogn ise that no solu­ tion exists if that is the case. 2. Alpha-beta algorithm. An algorithm fo r finding the minimax s o lu ­ tion of a tree with the minimum possible effort. This algorithm is at its most efficient when the branches of the tree are examined in the o rd er of their m e rit. A backward pruning technique. 3.

Alpha-beta cut-off. P a rt of the t r e e is cut off (or pruned) by the alpha-beta algorithm if it is shown that examining that part of the tree cannot be fruitful.

4.

A r c : A representation of a game move.

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5. A ssem b ly cod e. The code in which assembly language is written: The latter is closely linked with machine code, but made e a s ie r for the p ro g ra m m e r by the aid of labels and mnemonics: known as 'l o w - l e v e l ' or 'basic' program ming. 6.

Backing-up, backed up. A method of assigning a value to a given position, by working backwards from the end positions of the tree of p ossib ilities which the origin al position can generate.

7. Backward pruning. Methods of eliminating the evaluation of irre le v a n t positions and variations, while the search tr e e is being developed. 8.

Bit. Contraction of the words binary digi t , i.e. 0 and l , t h e two numbers used in binary notation: te rm has spread to c o v e r the representation of a binary digit (e.g. an element in machine core):

9.

B re a d th -first s e a rc h . A tree search which fir s t examines all nodes at le v e l 1, then all at le v e l 2, and so on.

10.

Byte. Set of binary digits handled as a unit, usually a sub-division of a ivord.

11. Cut-off. See alpha-beta cut-off, also backward pruning. 12.

Central processin g unit ( C P U). Co-ordinates and controls the activities of other units of the computer and p e rfo rm s all arith­ m etic and logical operations applied to the data.

13.

C R T . Cathode ray tube.

14. Dead/quiescent position. A position is said to be dead or quiescent if no captures or checks are possible. It is assumed by most p r o ­ g r a m m e r s that such positions may be evaluated by a scoring function, thereby giving an accurate assessment of the m e rit of the positions. The assessment would be m ore accurate if in addition, no d irec t threats w ere possible. 15.

D epth-first search. The search t r e e is grown fro m the top p osi­ tion along one single 'branch'. When the search can go no deeper on this path, it returns to the le v e l above and grows the next sub­ branch. Essential if alpha-beta pruning is to be used.

16.

Entropy. Concept taken from thermodynamics. The entropy of a system is a measure of its d egree of 'd is o rd e r'.

17.

Evaluation functions. A device that determ ines a single numerical value for a board position, intended to r e fle c t its good or bad features.

18.

Fan-out param eter. The number of plausible moves considered at each le v e l in the search tree.

19.

Forw ard pruning. Any method of reducing the alternatives to be considered before the search proper is begun.

20.

Heuristic. A c rite rio n of action that aims to make it e a s ie r to find the solution to a problem by concentrating the search along hopeful lines of investigation. Can be used to imply 'rule of thumb' and/or 'not always r e lia b le '.

21.

H ig h -le v e l languages. P ro b lem -o rien ted , rather than machineoriented program m in g language. Instructions may take the form

Jean Hayes

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of fa ir ly complex statements which are then translated into machine code. 22.

Horizon effect. A p rogram faced with what is in fact an inevitable loss of m aterial w ill often d efer this loss by inserting a useless check or the s a c r ific e of m ore material. In this way the moment of doom is pushed o ve r the horizon, out of view of the p r o g r a m ’ s search. The program then ends up in an even w o rs e situation. The horizon effect can also manifest its e lf in the opposite way, i.e. by making unattainable some la r g e r gain by grabbing sh ort­ sightedly at a m o re immediate but le s s e r gain which happens to be within the p r o g r a m 's lookahead horizon.

23.

Input-output. The transfer o f information from the human operator to the machine back to the human operator. Input-output d ev ic e s include such things as teletypes, punched paper tape re a d ers, punched card readers, visual display units etc.

24.

K i lle r heuristic. If a certain move is found to refute a m ove under consideration then this 'refutation m o ve' is tried fir s t when e x a m i­ ning other m oves at the same level. In this way, if a program notices that its queen can be captured if it makes some particular move, it w ill look f ir s t to see if its queen is safe when it is con si­ dering alternative moves.

25.

Lookahead, (see Tree-search)

26.

Machine code. Symbols (numerical) which make up machine lan­ guage, i.e. the language than can im m ediately obeyed by a particu­ lar computer, without any intervening change or translation.

27.

Minimaxing. A method of assigning a value to a given position by alloting it the maximum or minimum value of its successor p o s i­ tions according to whether our side has control of the m ove (m axi­ mum value) or our opponent does (minimum value).

28.

Node. A representation of a position in a game.

29.

P a ra m e te r. A dimension or other quality which can be varied during consideration of a problem.

30.

Plausibility analysis. By employing various heuristics it may be possible to determ ine which of the possible moves a re most worth considering. The remaining m o v e -p o s s ib ilitie s can then be f o r ­ gotten about, or examined at a later stage if desired. An example of forward pruning.

31.

Ply. Move by one side, a 'h a lf-m o v e '.

32.

P r o g r a m . A sequence of instructions (in machine, lo w -le v e l, or h igh -level language) which causes a computer to c a r r y out a s e r ie s of operations.

33.

Pruning. Cutting off a proportion of the branches of a search tree so as to avoid needless work. If it can be safely conjectured that the solution does not lie in a certain part of the tree then that part of the tree may safely be ignored.

34.

Refutation move. One whose calculated value makes consideration of part of the search tree irre le v a n t (see K ille r heuristic)

35.

Scoring function, (see evaluation u f n ction)

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36. Subroutine. A part of a program with a distinct function. 37.

T r e e - s e a r c h . The search fo r a solution to a problem by examining the branches of a 't r e e of p o s s ib ilitie s ’ . The associated nouns search, search-tree, and lookahead are used almost interchange­ ably.

38.

Turbulent position. A position is turbulent if captures and checks are possible.

39.

Visual display unit (V D U ). Device using cathode ray tube to display information from the computer.

40. Word. A 'convenient' number of bits, which are processed as a unit. W ord length v a r ie s with different machines and may be fixed or variable.

5. Notes on the Competing Programs The mechanisms described in the last chapter w e re used, almost with­ out exception, by each of the thirteen p rogram s competing in the W orld Computer Chess Championship. However, plausibility analysis was omitted in some cases: for example, the CHESS 4. 0 p ro g ra m m e r s found that it was cheaper in term s of computer time and space to do without it. Backward pruning by means of the alpha-beta algorithm was used by e v e r y program except Hungary's P A P A , but there w e re variations and additions in points of detail. The general philosophy of all current chess p ro gram s is based on e x ­ tensive search and efficient pruning, and we comment on this in the next chapter. The Soviet w o rk e rs are possibly taking a m ore mathe­ matical approach, concerning themselves with the abstract principles of tree structures, etc., while others use m ore ad hoc methods. Search procedures, of course, are not them selves concerned with chess: the evaluation function is that part o f a program in which specific chess knowledge is embedded. Evaluation functions are bundles of w e l l- t r ie d chess heuristics and bear a strong fam ily resem blance to one another. P A P A (Hungary) and FREEDOM (Norway) have attempted to use a unitary concept, but m a terial is usually the dominant factor. The 'co n ­ ventional' values used are: pawn = 1, knight = bishop = 3, rook = 5, and queen = 9, as already mentioned. The king either has no value— since he always remains on the board—o r e ffe c tiv e ly infinite value: the latter is m ore usual. The p rogram s d iffer in o v e ra ll organization, data structures, computers and program m ing languages used, and such things as game and tourna­ ment experience. They also d iffe r in the number of man-months e x ­ pended on their development, with a range of about 7-70. It is an un­ fortunate fact that industry, government laboratories and u n iversities tend to re gard computer chess as frivolous, if elegant, so that many p rogram s have been developed in spare or even stolen time. The Soviet Union is fortunate in this respect, for computer chess appears to be regarded there as a legitim ate academic study and to be under­ written with adequate funds. It was hoped that the Soviet win would needle other nations into investing in computer chess but so far there seem s to be little sign of it! The entries for the world tournament came from the two continents of Europe and North A m eric a , and we describe the individual p ro gram s within these two categories. Our thanks go to the p ro g ra m m e r s who have helped us, with answers to questionnaires, personal in terview s and their own notes. The authors of CHAOS, CHESS 4. 0, and THE OSTRICH (all from USA) provided us with existing technical m a te ria l which is r e ­ printed la rg e ly unchanged. The description of THE OSTRICH com es from Dr M. Newborn's publication, The ACM 1972 Computer Chess Booklet, to which the interested reader is r e f e r r e d for g re a ter detail about this and other program s, and also a w e ll-w ritte n account of computer chess in general. Although TH E OSTRICH has changed in the last three years, the 1972 vers io n was competing at Stockholm: a p ro g ra m m er usually p r e fe r s to enter his best tested, rather than his newest, program in a tournament.

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E U R O PE 1. Austria: F R A N T Z The author of F R A N T Z is Dr G. W olf of Rechenzentrum Graz, Graz, Austria. He d e s crib e s his program b riefly as follows, breaking it down into three structures or levels: '1. At the f ir s t le v e l there are multiple exchange routines concerned only with captures and recaptures, the alpha-beta routine being used without depth limitations. Evaluation is based on (a) the calculation of approximate m a te ria l value, and (b) the calculation of attacking moves. '2. The second le v e l is the tactical search algorithm (one player is the attacker, the other looks for re p lie s ) which searches the tree for forced and fo rcin g m oves, to attain or prevent m a teria l or positional gain or loss. '3. The third le v e l is the master routine which looks fo r book openings (only a few have so far been stored) and special endgame moves, i.e. it activates simple mating sequences.' The program was one year in development before it competed at Stock­ holm and had no previous tournament experience: it was seeded number eleven, and improved on expectation by finishing equal fifth with B E AL, M A S T E R , THE OSTRICH, and TE C H II. F R A N T Z was written in Assem bly language and in F O R T R A N for the U NIVAC 494 computer. It occupies 32K of 30-bit words and was run on a Stockholm machine for the tournament. 2. Hungary: P A P A The program was produced by G. Rajna (a Hungarian Chess M aster) and L. Alm asi of the Hungarian Academy of Sciences (Budapest) in approximately six months. It had played about five games of chess before entering the tournament. P A P A has some extre m ely unusual features, e. g. the alpha-beta pruning technique is not used, and evaluation o f a position is based on the single concept 'entropy'. T h ere are no stored book openings. The following general notes w e re provided by M r Alm asi, and translated by Dr G. K iss and Dr J. Kalan: 'Th e basic theory on which P A P A is constructed is that there exists a general characteristic of the game of chess, namely the concept of entropy. 'T h is concept has been employed in physics for a long time. In the case of a gas, it is the logarithm of the number of those m icroscopic states compatible with the m acroscopic param eters of the gas. 'What does this mean in te rm s of chess? A common characteristic of e v e r y piece is that it could move to certain squares, including by cap­ ture. In any given position, therefore, the pieces by the rules of the game possess certain states, only one of which w ill be realized on the next m ove. The d ifferen ce of the logarithm of the numbers of such states f o r Black and White re sp e ctive ly is the "entropy of the position". The task of the computer is then to increase this value for its own benefit. 'E v e r y chess player knows that the m ore mobility his pieces have and

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the m o re constrained are his opponent's, the better his position. For example, checkmate is the best possible state for the attacker, and the chess program playing according to the above principle without the p rio r notion of checkmate w ill automatically attempt it if possible. 'Entropy is a principle of statistical physics and th e re fo re is only applicable in statistical contexts. The number of m ic ro sta te s of a con­ fined gas is v e r y large and th erefore the statistical approach is valid. In chess, however, the number of pieces, a m acroscop ic param eter, is v e ry sm all and therefore in this context the "v a lu e " of a position can­ not be an exact function of entropy. For example, it is possible to checkmate with a total fo rc e of a single pawn despite the fact that the opponent has many pieces and various positions available. 'Exam ples of s a c r ific ia l combinations further demonstrate this con­ sideration. T h e r e fo r e we also need specific information about any given position. For example, entropy could be m axim ised by White giving check, but if the checking piece is then taken the m ove was a bad one. The logarithm of the number of variations which have been examined in this way gives the amount o f information. In the endgame it is rather inaccurate. Because of the sm all number of p ieces the above-noted inadequacy of the statistical principle becom es evident. At the moment the program has no separate routines for endgames. 'The depth of the search tree can be varied. Accordin g to experience so far, in the opening and middle game a s ix -p ly lookahead is suffi­ cient. A lookahead of ten does not increase the quality of play p r o p o r ­ tionately with the increase in processing time. (About 1000 nodes are examined per move.) 'Th e program only examines those steps on the tree which give large values. A fte r a given depth it only examines captures and check p osi­ tions.’ The p r o g r a m 's pre-tournament play was im p re s s iv e enough to earn it the position of third seed, but it finally finished in twelfth place, equal with A16CHS. We have already commented on this disappointing and unexpected result in chapter 2 (game 3). P A P A was written in F O R T R A N and occupied 30K. During the tourna­ ment it ran on the CDC Cyber 73 at Studsvik, Sweden. 3. Norway: FREEDOM This program (seeded tenth) bears certain resem blances to P A P A in the emphasis placed on a single feature, mobility. FREED OM is the work of P r o fe s s o r N. B a r ic e lli, from the U n iversity of Oslo, who has been developing it as a s p a re-tim e e x e r c is e over a period of approxi­ mately two years. O riginally, mobility or 'fr e e d o m ' was the sole factor taken into account, and was defined as the number of m oves open to the program divided by the number of m oves open to the opponent. This was later found inadequate for evaluation, so that conventional m a teria l values w ere added to the scoring functions. However, the deeper the search, the m o re m obility is stressed r e la tiv e to m a te ria l in the evaluation. A l l fo r m s of plausibility analysis are omitted but backward pruning is c a rrie d out by means of the alpha-beta algorithm. T h e re are no stored book openings in FREEDO M and the only change for endgame play is to increase the depth of search as the alternatives become few er.

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The program was developed on the Cyber 74 at K je lle r , Norway, and occupies 20K 60-bit words. It is written partly in Assem b ly language and partly in F O R T R A N . Stockholm result: equal tenth with S w itz e r­ land's T E L L .

4. Soviet Union: KAISSA The Soviet program is rom antically named after a wood nymph, Caissa. She was the creation of the great orientalist Sir W illiam Jones, who in 1772 published a poem of great dullness about the unsuccessful wooing of C aissa by the god M a r s . A kindly naiad suggested that Caissa might relent if M a r s could produce some new diversion, and the result (a cooperative e ffo rt of Sport and the God of W a r !) was the game of chess. The following lines d escribe the knight’ s m o v e , and eloquently convey the flavour of the p o e m : . . . Nor friends nor foes their rapid fo r c e restrain By one quick bound two changing squares they gain: F ro m v aryin g hues renew the f ie r c e attack And rush fro m black to white, from white to black . . . But if the poem is pedestrian, the program is ex tre m ely interesting and was the o v e r a ll winner at Stockholm. KAISSA itself is the result of about fiv e y e a rs of e ffo rt on the part of a large team which includes V . L . A r la z a r o ff , G. M. A d e ls o n -V e ls k ii, A. R. Bitman (who is a Chess M a s te r) and M . V . Donskoy. M e m b e rs of this team have been working on computer chess, both th e o retica lly and p ractically, since the 1960s but there is not a great deal of information about the work in western scientific publications. One of the papers which is available (A d e lso n -V els k ii et at. 1970) d e s ­ c rib e s the program as it was in the late 1960s and from the evidence available it is likely that KAISSA has many of the same features. O v e ra ll structure can be considered in four segments: 1. External segm en t, concerned with the type of 'schema' which is used (see below), the type of game (machine with machine or man with machine),* and input-output devices. 2. Control segm en t, concerned with tre e -s e a rc h in g and pruning, and, when the s o -c a lle d active schema is being used, the 'safety' and the 'a c tiv ity ' of a move. 3. Evaluation segm ent, fo r determining and scoring the relevant factors of a position. 4. Technical segm en t, fo r generating legal moves and all updating after m oves have been made. T h is paper has notes on the evaluation function; the present function is lik ely to be s im ila r, if not identical. Bonus points a re given for: 'A phalanx’ , i.e. two pawns side by side, on ranks 4-7 fo r White, and ranks 5-2 fo r Black. T h r e e pawns side by side count as two phalanxes. Centre pawns.

* A s fa r as we know no other program makes this particular distinction. H o w e v e r , there a r e no details of changes made, if a n y , f o r the two modes of play.

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Pawn attack on the centre. Passed pawns. 'S c o p e ', which is the calculation of the influence that each piece e x e rts on all squares, occupied or unoccupied by either own or enemy p ieces. Attack on undefended pieces and pawns on squares adjacent to the king. •

Attack by a minor piece on a 'hole' (weak square). A hole is defined as a square, on squares 1-5 fo r white and 8-4 for black, under attack by an enemy pawn, undefended by own pawn and with no chance of defence even after pawn advance. M inor pieces standing in an opponent's hole. Knights in the centre. Rook on an open file , or threatening an open file. Castling. Penalties are incurred by: A hole. A weak pawn (one behind a hole). Isolated pawns. Doubled pawns. Pawns which are isolated and doubled. F o rfe itu re of castling. Opponent's castling. The re la tiv e weightings a r e so arranged that no combination of p o s i­ tional factors can compensate fo r the 'minimum m a terial p rep o n d e r­ ance', which is half a pawn. M a teria l values a re: pawn = 2 , knight = bishop = 7, rook = 10, queen = 20, with no value f o r the king. The authors comment that changing these fa c to rs can m a te ria lly a lte r both the strength and character of the game, whereas changing the weights of the facto rs makes v e r y little d ifferen ce. A s KAISSA plays at the m om en t, there a re different evaluation functions fo r the middle game, the endgame and checkmate. T h e r e is a large book of stored openings, over 10,000 positions, which is la r g e r , by an o rd e r of magnitude, than any other competing p r o g r a m . T r e e search in g: The program can grow its lookahead tr e e accordin g to two different 's c h e m a s ', an absolute or an active schema. If the p r o ­ gram is playing according to the absolute schema all legal moves are considered up to some fixed depth, say fiv e ply. T h e r e a fte r only fo rc in g m oves a re considered, a fo rcin g move being defined as a check, a rep ly to a check or an e ffec tiv e capture ( i . e . one which does not provoke a s e r ie s of meaningless captures). Methods of search termination a re also applied of parts of the tr e e where a large m a terial advantage has developed. The active schema is concerned with forw ard pruning of the tr e e , and is c a rrie d out by considering only active (or safe) m oves. A m ove is term ed active in a case such as the following: In the lookahead, White makes a move and Black ’passes' o r makes a blank m ove. If White in

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the next move (in effec t having two moves in succession) can gain m a terial advantage by fo rc in g moves (checks, r e p lie s to checks, and captures), then such a move is active. A c tiv e moves thus constitute an extension of the concept of fo rc in g moves and can be thought of as immediate threats. The search tr e e grown in this way is much 'skinnier' than that grown by the absolute schema and hence can search to a much deeper le v e l. Interesting as this schema is, it was not actually in use during the p r o g r a m ’ s play at Stockholm. Backward pruning is done f ir s t and fo re m o s t by the alpha-beta algorithm combined with what is called a 'b e st-m o ve s e r v i c e ', which works as follow s: At any given depth in a search tr e e the ten best moves arisin g from a position a re stored. When another position at the same depth is r e a c h e d , those ten moves a re considered immediately, after possible checks and captures. Then a new list is compiled of the ten best moves drawn from both positions, and this is considered at the next position of the same depth and so on. This is a way of communicating information from one branch of the search tr e e to another. T he most interesting pruning technique is 'the method of an a logies’ , which attempts to a ssess mathematically the essential s im ila rity of positions. If this can be done it obviously cuts down search by grouping positions into classes or categories, and the method works as follows: Suppose a move is an im m ediately losing one in a given position, and we know the refuting variation. T h e r e may be 's im ila r ' positions, not n ec e ss a rily at the same depth in the search tree, where the same move is refuted by the same variation. Sufficient conditions for this are: (a) if the m aterial evaluation of the two positions is the same; (b) if all the moves adm issible in position one a r e also adm issible in position two; and (c) if the refuting variation is not 'influenced' by any differen ces between positions one and two. The concept of 'influence' is the most complicated, and is still being defined as work on the program con­ tinues. T h e o re tic a lly , influence is computed at the moment by c o n s id e r­ ing such points as positional d ifferen ces, squares that come under attack, squares that a r e relea sed from attack, and squares from which checks may be given as a result of moves of the refuting variation, move-paths of long-range p i e c e s , and also pins. These conditions are thought to be too strict in setting up analogies, but present work is p r o ­ ceeding along these lines. A sim plified version of this pruning method was in use at Stockholm, but has not yet been com pletely implemented. KAISSA played some fifty games b efore competing but had had no p r e v i ­ ous tournament experience. The 1972 version of the program played a consultation match by correspondence (no time controls) against the re a d e rs of Komsomolskaya Pravda. KAISSA lost one game and drew the other, a result which should be set beside B o ris Spassky's c o r r e s ­ pondence match against the same group of read ers: the fo r m e r World champion won one game and drew the o t h e r , thus demonstrating that Pravda re a d e rs a re no pushover. The program was written fo r the I C L 4-70 in A ssem b ly code, and occupies 384K bytes (8 -bit w ords). It could not be run on a Stockholm I C L machine because of some idiosyncracies of the Soviet operating s y s t e m , and it ran on the machine in Moscow where it was developed, via a telephone link.

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5. Switzerland: T E L L Named a fter the Swiss national hero, W illiam T e l l , this p rogram was produced by Johann Joss o f the Eidgenossische Technische Hochschule, Zurich. It has been a s p a r e - t im e activity and taken nearly two y e a rs to develop. T E L L is designed to analyse a la rg e search tr e e , with a variable depth of lookahead. The author d escrib es it as follow s: 'The program has three c a te g o rie s of move: ca te go ry 1, capture of the p iece last moved with a piece of le s s e r value (only one move per le v e l); category 2, captures and moves out of check; and category 3, all other moves. The search lim its a re three ply fo r category 1 and four ply fo r ca tego ries 2 and 3. Eight ply is the maximum depth of search o v e r all c a te g o rie s. A variant of the alpha-beta cut-off is used to prune the search tree . 'Evaluation is based on m aterial, control of field s moving with the desired piece: it is easy to gain control of field s with the queen but queen moves often waste tim e .' T h e r e are no stored book openings and no special routines fo r end­ games. The program occupies 8K 16-bit words and is written in A s s e m b ly language. The computer used was a Hewlett Packard 2100,a machine sm all enough to be on the tournament site at Stockholm. O rigin a lly seeded tw e lfth , T E L L tied with FR E ED O M in tenth place. 6. United Kingdom: (a) A16CHS T h is B ritish program was one of the two produced neither by a government laboratory nor an academic institution (CHAOS was p r o ­ duced by w o rk ers at U N IV A C ). A16CHS was developed by R. P rin sen of InterScan Data Systems, Hounslow, in seven months. It was seeded ninth at Stockholm and finished in twelfth place, equal with Hungary’ s PAPA. 'The evaluation function is a combination of positional fa c to rs (m o b i­ lity and square c o n t r o l), attack and defence. The p r o g r a m 's tr e e search goes to a depth of three ply, but the depth can be controlled by the amount of time available. Initially a one-ply search is made, capture p ossibilities a r e noted and moves are ord ered in p r io r ity according to the values given by applying the evaluation function. A further search continues to two ply, f i r s t - p l y moves being slowly eliminated while the program continues a deeper search .' T h e r e are no stored book openings and no plans f o r incorporating any into the program . On the other hand special routines fo r endgames w ill be added, although there w ere none at Stockholm. A16CHS was developed on a Computer Automation Alpha 16 m in i­ computer and occupies 11K at present. H ow ever, it is in a continuous state of growth and development. 7. United Kingdom: (b) B E A L The author of the B E A L program (seeded thirteenth at Stockholm) is D. Beal, a post-graduate student at Queen M a r y C o lle g e , London University. It has taken about one ye a r to develop, and work is still continuing on it. He gave us the following notes about the vers io n which played at Stockholm:

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’ A t its present stage of development, the program searches a tr e e of possible future moves and cou n ter-m oves based on an evaluation function fo r positions which includes m aterial, mobility of pieces and positioning of p iec es . The function applies slightly different c r it e r ia to opening and middle game positions (no stored openings) but the end-game is not distinguished from the middle game at present. 'The search tr e e does not com p rise all moves and counter-m oves: m oves not considered likely to influence the evaluation function favourably a r e omitted and the search is not continued beyond p o s i­ tions considered to be hopeless fo r one side or the other. T h e re is a depth lim it beyond which search is not continued in any circumstances but many lines of play examined stop b efore this. ’Within the evaluation function d escrib es a b o v e , the determination of the m a teria l value includes an examination of the effects of captures and counter-captures, in s im ila r fashion to the o v e ra ll search. ’ The program is written mainly in F O R T R A N with some parts in COMPASS, the A s s e m b ly language fo r the CDC 6000 s e r ie s of c o m ­ puters on which the program is run. It occupies 20K 60-bit words of c o re store when executing.’ T h is program tied fo r fifth place with F R A N T Z , M A S T E R , THE OSTRICH and T E C H H. 8. United Kingdom: (c) M A S T E R M A S T E R , designed by P. Kent (Atlas Laboratory, Chilton) and p r o ­ gram m ed by J. Birmingham (Atomic Energy R esearch Establishment, H a rw ell) has evolved through s e v e r a l different versions, all based on a p ro gra m written by A. Bell (Rutherford Laboratory, Chilton) eight y e a r s ago. The search has increased fr o m two to four ply, and six ply was used at Stockholm (since when it has increased further). The twoply vers io n played about 100 games, the fou r-p ly version ten and the six -p ly version two. M A S T E R had no pre-Stockholm tournament e x ­ perience. T h is p rogram , like the Soviet p rogram , lays m ore emphasis on tree searching techniques than on the evaluation function, which is r e l a ­ tiv e ly sim ple. It takes into account the conventional m aterial values (no value fo r the king). T h e r e is encouragement to swap off when m aterial values a re evenly balanced and an incentive for minor pieces to attack p ieces of higher value. A s a piece on its own home square initially has less value than elsew h ere there is an incentive fo r quick development. A s with most program s there is a bonus fo r castling. Centre values are high to begin with but the emphasis shifts fro m the centre as the game p ro g re ss es . The moves a re ord ered at each ply by the evaluation function to aid the later alpha-beta pruning. T h is face evaluation is also used fo r a somewhat risky form of forw ard pruning known as ’ r a z o r in g ’ . As backed-up values a r e r e c e iv e d they a r e compared with the face evaluations of the next move in the list. The new move is examined further by the t r e e - s e a r c h e r only if its static value is higher than the backed-up value, plus or minus some e r r o r estimate. This can speed up the search by a factor of about ten. Another pruner, ’ the chopper’ , ensures that if there is only one legal move open to the program it makes it at once without further search. This mechanism may sound obvious, but TECH II which has nothing equivalent took seven minutes in round one to find its only available move.

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Optimal sequences a r e saved on each move and examined fir s t . If this 'f e e d - o v e r ' a r r a y contains a good sequence the alpha-beta prun­ ing is e ffe c tiv e much e a r l i e r . In such a case the number of nodes examined may be lessened by a factor of four or fiv e , while the housekeeping costs of 'f e e d - o v e r ' a re v e r y much less (approxim ately three per cent). M A S T E R makes use of stored book openings, and at the time o f the tournament there w ere 280 lines, each ten moves deep; this number is still being expanded. In the endgame the heuristic is 'd riv e the king to the c o r n e r ' . The program is written in PL1 and occupies 150K bytes. The p r o ­ gram was run fro m Chilton's IBM 370/195 at the Rutherford Lab., and it finished in fifth place along with F R A N T Z . B E A L , THE OSTRICH, and TECH II.

N O R T H A M E R IC A 9.

Canada: R IB B IT

R IB B IT was the only Canadian entry: it was developed by G. Calnek, R. Crook, R. Hansen and J. P a r r y , all students at the University of W a t e r lo o , Ontario. The description of the program which follo w s is based on notes supplied individually by Hansen and P a rry . R IB B IT uses a tree-stru ctu red lib ra ry of approximately 2000 stored book openings, including the Sicilian, Ruy L o p e z and Nimzo-Indian. When out of its book, R IB B IT grows a search t r e e n moves ahead and decides on the best of the possible m oves. Evaluation of ’b e s t-m o v e s ' is judged with a scoring function which takes into account such things as pawn structure, mobility, m aterial and many r e la t iv e ly minor things such as preventing the opponent from castling. A few changes a re made to the evaluator when the program reaches the endgame. The program uses ' n-best' forward pruning. At each node in the search tr e e a routine E V A L examines all the possible moves and gives them two values. The f ir s t is the 'look at me f i r s t ’ value, which giv es high rating to captures and other threatening moves; the second is the actual value assigned to the move, which includes the gain or loss in position which the move would produce. Doing incremental positional evaluation is somewhat faster, but less a c c u ra te , than doing it fo r a total board position. A fte r this the 'n-best' moves a re searched as part of the tr e e , which is trim m ed by an alpha-beta pruner. Some 40 nodes are examined p er second, 5, 000-10, 000 per move. D ifficu lties can occur with outpost knights and pawns about to queen. F ro m R I B B I T 's point of view , it is better to capture the opposing pawn a fter it has queened. Further, R IB B IT has no m em o ry of p reviously encountered p o s itio n s , and thus it always makes the same move in any given position. The program was written in F O R T R A N and occupies 23K, 36-bit words on a Honeywell 6060. It had played about thirty gam es p r io r to the world tournament, winning the f ir s t Canadian Computer Chess champion­ ship, and it took third place at Stockholm after being having been seeded seventh. It is c le a r ly a strong p rogram , and went on to win the A C M 1974 Computer Chess tournament at San Diego.

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10. United States: (a) CHAOS The authors of CHAOS a re I. Ruben, F. Swartz, J. Winograd, V. Berman and W .T o ik k a of Sperry Univac, Cinnaminson, New J e rs e y . They began work on it in 1972 and entered the program fo r the 1973 A C M Computer Chess Championship, where it tied fo r second place. Later it earned a provisional USCF rating of 1493 in a five-round Swiss (human) tourna­ ment. At Stockholm it was seeded fourth and placed fourth. The fo llo w ­ ing is a digest of available technical m aterial. CHAOS may be divided into fiv e major segments: 1. Main control. The main control accepts a move, determ ines the response via the tr e e -s e a r c h in g section and displays the response. D e s c rip tiv e notation is norm ally used but CHAOS also accepts a lg e ­ braic notation. 2 . Command processing. T h e r e a re currently fo rty -th re e commands which control displays, save and re s to re games, act as tim ekeepers, control the p ieces on the board and the modes of operation (such as setting the current side to Black, say, and asking for a draw, etc.). A further group of commands is concerned with debugging the program . 3. T r e e sea rch in g. T his is basically done with a depth-first alphabeta minimax algorithm (see chapter 3). Intermediate level moves are o rd ered to speed up the pruning, and the ordering makes use of the k ille r heuristic (i.e. saving refutation moves and looking at them fir s t ). A complete analysis is made fo r the fir s t two ply, and this is used for p r e - o r d e r in g before the search proper begins. CHAOS can use either a fixed depth of search (usually five ply for tournaments) or a variable depth search where captures, checks, p r o ­ motions, etc., a re investigated fu r t h e r , usually between four and nine ply. Interestingly enough, the fixed depth analysis has so far turned out to be superior. F orw ard pruning is controlled by a param eter F A N . F rom any given position no m ore moves are examined a fter F A N number of non­ productive consecutive moves, where 'non-productive' means no improvement in backed-up values. When the ord erin g has been good, as few as (F A N + 1) moves w ill be examined at each position, but when it is b a d , all moves may be examined. The program usually plays with a value of F A N between 3 and 6 and looks at no m ore than ten altern a­ tive moves fro m any position. Values fo r F A N and also fo r depth of search a re chosen b efore the lookahead on any move begins. These a re based on tim e consumed in last tr e e analysis, total time remaining, speed of machine, C P U a v a ila ­ bility and so on. 4. Evaluation function. The evaluation function E V A L p e rfo rm s an evaluation of a board position r e la tiv e to one side. This single number is: value(side) E V A L (s id e ) = 1000 x --------------------------- ------------------- value(side) + value(opposite side) Thus an evaluation of 500 means that both sides have equal positions, 0 means 'our' side is checkmated and 1000 that the opposite side is checkmated. Nineteen facto rs are taken into account, and their weights modified according to the stage reached in the game:

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Threatened pieces, the sum of the value of a ll p ieces which have enemy pieces bearing down on th e m , but not n e c e s s a rily en prise. Capturing p oten tial, an 'adjusted' sum of the value of capturing poten­ tials on all squares on the board. M o b i l i t y , defined as the number of legal m oves. Centre control, which c o v e rs both occupancy and attack on centre squares and reduces in importance as the game p r o g r e s s e s . Pins and d isco vered checks. M a te ria l, which contributes the greatest amount to the evaluation. Values a re the conventional ones with no value assigned fo r the king. Queen d evelop m en t, a penalty for developing e a rly . Double threats and captures. Double threats c a r r y the value of the second most valuable piece able to be captured by the moving side, on the grounds that if two pieces can be attacked, the low er valued one w ill be captured. Captures represent the total value of p ieces m ore strongly attacked than defended. T h is is also an ’ adjusted’ value which attempts to approximate the net value to the side moving, a fter an exchange has taken place. Attacked pieces, the total number of p ieces attacked m ore strongly than defended. Rook usage, which rew ards castling, doubling of rooks, occupation of open file s and rooks behind passed pawns. M obility potential, a measurement of the legal moves as w ell as the ’ not quite le g a l ’ moves (e.g. moves which guard, or would have been legal if out of check, or which bear through and along the line of attack of another piece, etc.). T h is c a r r ie s less weight than m obility p roper. Pawn usage, which includes pawn advancement, totally or p artia lly unblocked pawns, connectedness, doubled pawns, etc. King endgame position. T h e r e a re rew ards fo r fo rc in g the enemy king to the edge, stopping an opposing unblocked pawn, staying within the ’ square' of the opponent’ s passed pawn, and king opposition, etc. Development. The e a r ly development of minor p ieces is encouraged. Queen pins, which counts p ieces pinned against the queen as w ell as discovered attacks on the queen. Attack on king. T h e r e is a rew ard fo r attacking close to the opponent's king. Best capture, the value of the highest valued p iece left en prise a fte r a move. King safety. T h e r e a re incentives fo r attacking c lo s e to one's own king. The evaluation function has been based as fa r as possible on general p r in c ip le s , avoiding special cases. F o r testing purposes the weights of these factors w e re set d ifferen tly fo r each side while the program played against itself. T h is yielded valuable information about best settings. (See notes on KAISSA fo r comments on their exp e rien c e.) 5. Opening p la y . CHAOS has a look-up f il e of ’ book' openings. F ro m a given position in the book file , if its opponent makes a move which is

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in the f ile , CHAOS makes the move which follow s in the stored s e ­ quence, f ir s t checking it for legality. If its opponent's move is not in the book file , o r the end of that sequence has been reached, the heuris­ tics take over. Move sequences may ’ branch’ to one another through the use of a 'transposition tag'. Book openings a r e used to avoid serious e r r o r s in opening play, to save t i m e , and to avoid complicating the heuristics in the main program . D ifferen t opening variations can be achieved by specifying the desired variation or by requesting random choice between the available options. Width of opponent choice has been considered m ore important than depth of moves in a sequence. Frequently CHAOS' book responds to ir r e g u la r but playable moves by attempting to transpose back to its main lines rather than attempting a refutation. Unfortunately the lit e ­ rature in chess openings is based on Grandmaster play (USCF rating of m o re than 2400) and it has thus been necessary for the author (USCF rating 1900) to add responses fo r the 'unbooked' moves in o rd er to achieve the d esired width. A ls o a Grandmaster may be happy with positions that CHAOS' heuristics have difficulty in handling, such as a kingside fianchetto: th e re fo re these have to be avoided. Studies of CHAOS playing against itself, with only one side using the book, have been helpful, but the creation of opening books s till seem s m ore art than s c i e n c e ! 11. United States: (b) CHESS 4.0 T h e s e notes have been provided by the authors of CHESS 4. 0 , and are quoted with minor modifications only: 'CHESS 4 .0 is written in assem bly language (COMPASS) fo r Control Data 6000 or Cyber s e r ie s of machines. In its normal mode of o p e ra ­ tion the program accepts its input from (and sends its output to) a t i m e ­ sharing term in al. Input is in the form of chess moves in descriptive notation or special commands, and output consists of moves in d e s c r ip ­ tive notation plus diagnostic information. 'The authors of CHESS 4.0 a re L . R . Atkin and D.Slate of Northwestern U n iversity, Evanston, Illin ois. This program borrow s many ideas from e a r l i e r p ro gram s by the authors (i.e . CHESS 2. 0, 3. 0, 3. 5 and 3. 6) and does not represent a m ajor conceptual advance o ve r them. H owever, it is an entirely new p rogram , written in 1973. Its playing strength is somewhat g re a te r than that of CHESS 3. 5, and it im proves o ver e a r lie r v e rs io n s mainly in te rm s of modularity, ease of modification and efficien cy. 'B a s ic a lly the program does depth-first alpha-beta pruned searches of the move tr e e . The search is depth-first in the sense that the whole game tr e e is not continually retained. P rev io u s branches can be (and in certain conditions a re) re v is ite d but only at the cost of completely regeneratin g them. A l l the heuristic move searching and position evaluation decisions a r e concentrated in one routine, called E V A LU 8. E V A L U 8 d ire c ts the p ro cessin g of a node in the tr e e . When it calls for a move to be searched, it w ill be called again at the next higher ply le v e l. Thus E V A L U 8 must be r e c u rs iv e and r e - e n t r a n t , because it is in simultaneous use at different ply levels. E V A LU 8 invokes modular n on -con troversial routines to up-date the data-base during t r e e searching. The data-base consists la rg e ly of bit-patterns describing the location of the p ieces and the squares they attack. E V A L U 8 itself

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is written mostly in h igh -level m a cros that re se m b le LIS P functions in syntactical fo r m . T h ese m a cros allow fo r a ccess and manipulation of locations of pieces, squares they attack, lists of squares with certain p r o p e r t i e s , and other types of data. T hey expand into r e la t iv e ly efficient code while saving the p ro g ra m m e r fro m problem s of machine r e g is te r a llo c a tio n , etc. 'The actual heuristics in E V A L U 8 a re p r im itiv e . The tr e e search is c a rrie d out as a s e r ie s of iterations, each of which is its e lf a complete full-width search to a fixed depth (subject only to alpha-beta pruning), with extensions beyond that depth only f o r piece-captu re sequences and in some cases sequences of checks. The f ir s t iteration goes to depth 2, and each successive one goes one ply deeper, using the main variation and final s c o re from the preceding iteration as a guide to gain e f f i c i ­ ency. The depth of the last iteration is determined either by a p a r a ­ m eter setting or, in tournament mode, by an automatic tim e control mechanism. With this mechanism in u s e , depths range from three to fiv e ply in opening and m id-gam e, and up to ten ply in the endgame. The use of a full-width search is a concession to the d is c o v e ry that fo r w a rd pruning heuristics (as opposed to alpha-beta backward pruning) such as those used in CHESS 3. 5 w e re too naive to justify the tim e spent on them. 'The endpoint position s co re s a r e based p r im a r ily on m aterial, except fo r the obvious cases of checkmate and stalemate. Each piece is given a standard value. The m aterial s co re is the sum of these values plus a second o rd er term that exp re ss e s the principle that it is advantageous to trade pieces (except pawns) when one is ahead in m aterial. T h e r e is also a special table of values fo r v e r y sim ple endgames; so that, fo r example, king plus bishop versus king is considered drawn. 'In addition to the m aterial s co re, te r m s a re added which e xp ress, in a p rim itiv e way, notions of mobility (number of squares attacked), pawn structure (passed, isolated, doubled, backward, e t c .), piece placement (e.g. rooks on seventh rank), and king safety (king in castled position, adequate pawn c o v e r ). In endgames in which one side has an o v e r ­ whelming advantage, separate heuristics are used which d riv e the opponent’ s king to a corn er of the board. E V A L U 8 detects position repetitions both within the tr e e and in a short history of actual m oves, and assigns the draw value to them. In addition, a heuristic that exp resses the fifty - m o v e rule is used. The s co re is pulled towards the draw value as one gets c lo s e r to fifty moves (both within and p r io r to the tr e e ) without a piece captured or pawn moved. On the a v e ra g e , the program s co re s about 300 positions per C P U second on a CDC 6400. ’CHESS 4.0 has a lib ra ry of opening positions and associated moves, which is consulted before the tr e e search is begun. If a match is found the associated move is played and no search is conducted. Currently CHESS 4 .0 's lib ra ry contains about 5000 assorted positions.' T his program was the number one seed at Stockholm ; it came second, and drew with the o v e ra ll winner, KAISSA, in the frien dly game played after the end of the tournament. 12. United States: (c) T H E OSTRICH G .A rn o ld and M .N e w b o rn of the Department of E le c tr ic a l Engineering and Computer Science, Columbia U n iv e r s it y , New Y o rk , have been w o r k ­ ing on THE OSTRICH since 1971 and the program described here,

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seeded sixth at Stockholm , has survived substantially unchanged since the A C M tournaments of 1972. This account is taken from M. New born’ s paper The ACM 1972 Computer Chess Booklet to which the read er is r e f e r r e d fo r g r e a te r detail. Functionally T H E OSTRICH can be considered in five segments: (a) an input-output and user communication segment; (b) a search tr e e and move generator segment; (c) a plausibility analysis s e g m e n te d ) an evaluation segment; and (e) a segment fo r all up-dating. Segments c and d take up the major part of the program . The p rogram makes use of three m ajor lists in its data structures: (i) M ove lists containing information as to the old and the new square and whether the piece is a capture; (ii) A list of squares that each piece controls; and (iii) A change list, which re co rd s changes necessary to back-up fro m any node in the tree to a previous node. Other lists d es crib e the game board, the location of the pieces, what pieces are pinned o r en prise , the most recent alpha-beta refutation moves, the current principal variation and all past positions since the last pawn move or capture (for the detection of draws by repetition). T r e e s e a rc h in g . THE OSTRICH searches a re la tiv e ly large t r e e , and extensive use is made of both forward and backward pruning. For e v e r y game a minimum search depth, a maximum search depth and an a v e ra g e move time are decided in advance. T ypical tournament settings would be four ply, six ply and 140 seconds resp ectively (the a v e ra g e move time is set at this level rather than at three minutes to allow f o r the time taken up by reading information in and out of the computer). Fanout p aram eters are also set before each game ( F 1 = 23, F2 = 20, F3 = 14, F4 = 9, F5 = 7, F6 = 6), and increased or decreased by one e v e r y third move according to whether the previous moves have taken m ore or less than the a verage move t i m e ; thus t im e - p e r - m o v e stays r e la tiv e ly constant. If the total time required to make three con­ secutive moves is less than the average move time, then both search settings a re increased by 2. In mid-gam e play, about 3000 terminal positions a r e evaluated per minute, and about 7000 per move. Search is usually to the minimum depth with captures and checking sequences followed out to the maximum setting. The fanout at the f ir s t level is around 2 3, but will exceed this if the program so far can see no p r o s ­ pect of avoiding the loss of a pawn or more. P lau sib ility a n a ly s is . A f t e r all legal moves at a given position have been determined, the moves a re scored and ordered according to their plausibility. T h r e e special r e - o r d e r in g routines are also u s e d , to help increase the number of alpha-beta cut-offs. Plausibility scorin g is as shown in the flow chart (figure 14), and va ries according to the piece and the stage of the game. Factors include captures (which r e c e iv e the largest basic s c o re and indeed terminate further analysis on that move), castling, advance, pawn threats, centre moves, rook moves, refutation moves, moves to safe positions when en prise, attack, and a factor whose usefulness it has been rather d i f ­ ficult to assess, ’the M i x e r ’ . Its job is to encourage moves by a large number of pieces, rather than repeated moves by a sm all number. The static evaluation function. T h is consists of thirteen subroutines each corresponding to a basic chess heuristic: M a te ria l. The subroutine which computes the difference between

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F ig u re 14. A flo w -ch art fo r plausibility analysis, showing the concepts (and the weights attached to them) that are used to pick out and o rd e r 'plausible' m oves to prevent the growth of unpromising branches of the search tr e e (after Newborn 1972).

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W h ite’ s and B la c k 's m aterial contributes the greatest single value to the o v e r a ll scorin g function. The p ieces have their conventional values. M a te r ia l ratio te rm , which computes whether an even exchange of m a terial has occurred between the top node of the tr e e and the bottom position being evaluated; a bonus goes to the side ahead in m aterial. Castling. Board control, which is intended to increase one's own mobility and r e s t r ic t one's opponent's. T h e r e is a small bonus fo r each square controlled, centre squares and squares near the enemy king have the greatest s c o re . 'Control' is defined as the ability of the piece in question to capture a hypothetical enemy piece on that square. T e m p i. M oving the same piece twice in the opening, moving a king or rook b efo re castling, moving a piece back to its immediately previous position and moving to a square in two moves when it could be done in one, all attract penalties. E a rly queen moves. T h ese attract a penalty before the eighth move of the game; by which tim e most minor pieces are developed and the king has castled. Blocking central pawns. 'Clogging' a position is penalised. Development of p ieces. Rapid development is encouraged by giving a penalty to unmoved minor p ieces or central pawns. Central pawns. These c a rry a bonus. Pawn structure. Advancement of pawns is encouraged and doubled pawns penalised. King safety. T o guard against king-side p ressure on the part of the opponent the program encourages its own pieces in its own k ing-sector. P assed pawns. The goal is to encourage the advancement and queening of pawns along with trading off the opponent’ s passed pawns before they become too advanced. A passed pawn r e c e iv e s credit according to its advancement. THE OSTRICH is coded entirely in S U PER NO VA assem bly language, which has the ability to p erform an arithmetic or logical operation, test the result and conditionally s k ip , all in one instruction. T h is is convenient, since chess p rogram s involve much conditional branching. T H E OSTRICH occupies 16K, 16-bit words of a Data General S U P E R ­ N O V A computer and played on-site at Stockholm. It tied fo r fifth place with B E A L , F R A N T Z , M A S T E R and T E C H II. 13. United States: (d) T E C H H T E C H II, the second seed, was written by A. Baisley, S. Kugell and R .W . Cooper of the A r t i fi c i a l Intelligence Laboratory at the Massachusetts Institute of T e c h n o lo g y , C a m b r id g e , M ass. The program came second in the A C M tournament of 1973, and some three months intensive work was done on it b efo re the world championship It is based on an e a r l ie r p r o g r a m , T E C H , written by J . G i l l o g l y , which had in its turn won second place in the 1971 AC M tournament. T his account is based on notes provided by A . B a is l e y . 'The program divides the game into fiv e phases; opening, middle game, endgames, pawn endgame and pawnless endgame. Different heuristics

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a r e used in the f ir s t four phases to determ ine the o rd e r in which the moves a re examined. T h is o rd e r in turn decides which move is played if m ore than one move has the same s co re s olely fro m the point of view of m aterial; for example, if there is m ore than one move available that neither wins nor loses m aterial. F o r pawnless endgames there is no p relim in a ry ord erin g of moves but the evaluation function includes in addition to m aterial, te rm s fo r centrability and proxim ity of the kings to one another. Thus the program can win with king and rook against king by driving the opposing king into the corner. 'The program uses a particular method of forw a rd pruning. If a p o s i­ tion has occurred previously in the t r e e (reached by a different set of moves, or by the same moves in a different o rd e r) its value is r e tr ie v e d from a 'hash' table. The value may cause an alpha-beta cut-off, so that no succeeding moves a r e examined from that position.' About 1300 nodes are examined per second and 234,000 per move. The program is written in A ssem b ly language and occupies 70K, 36-bit words, of a DEC P D P -1 0 computer. It tied for fifth place. CONCLUDING R E M A R K S Th ese thirteen computer chess p ro gram s a r e the strongest at present known to exist. Hopes and plans fo r the future a re described in the next chapter. A s a final note we should add that of the p r o g r a m m e r s them selves only two (D .B e a l of B E A L , and J. P a r r y of R IB B IT ) w ere prepared to predict that a program might reach International M aster standard by 1978.

6. Chess Thinking Shannon's proposals w e re aimed at constructing a chess program which could play a 'skilful' game of chess. If it be allowed that a middling club p la y e r plays a skilful game of chess—and which club p la ye r would d is a g r e e ? —then this target was reached at Stockholm. P r o g r a m m e r s have now become m ore ambitious: they want to produce a program which can compete at M a s te r le v e l. However, this looks unlikely unless there is a radical change of approach. Once it was thought that better search procedures, m ore intelligent pruning and m ore efficient evalua­ tion functions w e re all that was needed to bring about the necessary quantum jump in standards of play. P r o d ig ie s of energy and intellect have been expended on these things, yet D. Slate, one of the p ro g ra m ­ m e r s of CHESS 4.0, thinks that by taking advantage of e v e ry idiosyncra cy of a super-powerful computer at most 300 extra points could be gained on the United States Chess Federation scale. That would bring the best p rogram fro m a rating of approximately 1600 to approximately 1900, i . e . to the C lass A le v e l in term s of human play. The rating fo r the US National M a s te r is 2200-2400, and it is generally agreed that the gap between Class A and M aster is la r g e in te rm s of p erfo rm a n ce. Fu rth erm ore it becom es increasingly difficult fo r human p la y e rs to gain a further 100 points' worth of skill as they go higher up the scale. M .N e w b o rn (one of the authors of TH E OSTRICH) thinks that there are m ore than 300 points to be gained, but this is an exception to the widespread feeling among the p ro g ra m m e r s that computer chess perform ance, by present methods, is approaching a ceiling. Recently there have been suggestions that a special chess computer might be constructed (this was also, as was so much else, fir s t suggest­ ed by Shannon), the moves being 'w ired in' to the electron ic c ircu itry. T h is would speed up the calculations, perhaps by a thousandfold, and allow a m ore extensive search, but one would not expect to get more than a two- o r th ree-p ly extension. T h is is, of course, not to be des­ pised, and could be sufficient to give a M aster a few nasty moments in complicated tactical situations. But fo r the deep strategic thinking ch a racteristic of a M aster, additional program features of a radically different kind are required. What is it that makes the play of a computer program so different from human play? Apart from descriptions given explicitly o r im plicitly in the chess literature, there are one o r two excellent psychological studies of human chess thinking. The f ir s t of these was c a rrie d out at the turn of the century by A lfr e d Binet, m ore famous f o r the design of intelligence tests, who was concerned with identifying the particular mental faculties used by M a s te rs playing simultaneous blindfold chess. When Binet embarked on his investigation he believed that the feat depended on phenomenal qualities of visual m em ory, but after studying the reports sent to him by his chess M aster subjects he came to the conclusion that m em ory was only a small part of the story. F irs t, he put knowledge o r experience ('l'e ru d itio n '); second, imagination ( ' l ' im a gination); and third, 'la m e m o ire ': the latter was subdivided into 'm e m o ir e des id e e s ’ (abstract) and 'm e m o ire des sensations' (con­ c r e t e ). It turns out that chess M a s t e r s ’ mental images of a position are sur­ p risin gly abstract. Binet giv es an instructive diagram (figure 15) sent

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F ig u re 15. A M a s t e r ’ s visualization of the chess position shown (a fte r Binet's study, reported by de G root). by one of his subjects in answer to a request to draw his visualization of a certain position. On the left we see the position in diagram m etic form , while on the right we have the M a s t e r 's visual representation. Here it seem s that practically everything is lacking, including the colours and the outlines of the squares. The p ieces have gone. We are left with lines of fo rc e emanating fro m places where p ie c e s stood, and a set of numbers relevant to the dynamic possibility of a k in g-versu spawn race f o r the queening square. A m ore developed representation is constructed later in concrete term s, so that visualizing a position is not something that occurs all at once but is built up with different aspects predominating in successive steps. Bergson commented on Binet's experiments stressin g in particular the role of what Bergson te r m s a 'schema dynamique'; T his is basic to all mental skills, not chess alone, and is a complex structure of im ages and o r ideas that, while not itself susceptible of visualisation, provides the rules and fram ew o rk fo r it. Thus: 'The image of a board with its p iec es is not present in the m em ory of the p layer as it is in a m ir r o r , but at e v e r y moment it demands of the p la ye r an effort of reconstruction'. Excellent as Binet's studies were, de G ro o t's re s e a rc h e s o v e r the period 1945-65 are deservedly the most famous of all studies of chess thinking. He worked with p la ye rs at different le v e ls of skill, fro m Grandmaster to middling Club player, and studied them using the method of introspection; his subjects w e re asked to plan and think aloud when faced with chess positions taken fro m re la tiv e ly unknown M a s te r gam es. When the protocols w e re examined, all showed a somewhat s im ila r structure, which is outlined below: 1. F ir s t the p layer form ulates the problem, orients him self, and identi­ fie s the class the problem belongs to. Thus, with his f ir s t glance a good p layer is taking in what the position is all about and subsuming it under one or s ev era l well-known c a te g o rie s of p roblem . At this stage he is thinking strategically, i . e . in te rm s of v e r y general goals. 2. He starts to formulate m ore specific goals, and o rg a n izes his think­ ing in their direction. 3. He starts to calculate concrete variations (lookahead). 4. He form ulates partial outcomes and results, and checks p roced u res. Against the background of these stages de Groot s tr e s s e s a v e r y im p o r ­ tant concept, that of 'p r o g r e s s iv e deepening'. The good p la ye r returns time and again, and often fo r different reasons, to e a r l i e r lines of

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thought. T h ese he then p roceed s to develop further, seeing them in the context of new suggestions and insights. T his p ro c e s s is lacking from the procedu res of current p ro g ra m s. Of the four stages that de Groot unearthed in his experiments, the initial phase of immediate apprehension is the most striking, and dif­ feren tia tes the M a s te r and Grandmaster fro m the Expert. Thus, in de G r o o t's re c o rd s we find no significant d ifferen ce in phase 3 among p la y e rs of different ability. They all look ahead much the same number of m o ves. De Groot comments: ’ If this striking d ifferen ce (between m aster and expert)... is not rooted in tangible computable p ro p e rtie s of the actual thought p rocess, on what is it based? . . .on the fast and efficient problem formation and specialisation which d e riv e s fro m the (g r a n d )m a s te r s ' experience. He im m ediately knows what it is all about, in what direction he must search. He im m ediately " s e e s " the c o re of the problem in the p o s i­ tion, w hereas the expert p layer finds it with difficulty or m isses it com pletely. The master does not n ecessa rily calculate deeper, but the variations that he does calculate are m ore to the point; he s ize s up positions m o re easily, and especially, m ore a c c u r a t e ly . . . An entire position and a f o r tio r i an entire game are "ty p ic a l" to the master. A chess position is e asily recognized as one belonging to a certain class that can be handled in a certain specific way.' T h is description is reminiscent of Ian Hunter’ s study of the mathemati­ cian and calculating prodigy, Alexander Aitken. Among many illu stra­ tions of A itken 's immediate apprehension of the p rop erties of numbers, there is this small but illustrative instance. Someone mentioned the y e a r 1961 in Aitken's presence; he apprehended it immediately as 37 x 53, and 44 squared plus 5 squared, and 40 squared plus 19 squared. Hunter puts this facility down to the mathematician’ s ’e x p e rie n c e ’ in a sense that is identical with the te rm s in which Binet and de Groot d e s ­ cribe the chess M a s t e r 's most striking characteristic. Contrast this with the total absence fro m current 'lookahead' p ro gra m s of these pat­ tern recognition and d escriptive p rocesses, and also the total absence of long-range strategic plans, which, fo r a M aster, can easily span twenty to thirty moves, a distance fa r too great to bridge by detailed m o v e -b y -m o v e analysis. But above all, none of the current program s o ffe r the machine any possibility of learning fro m experience. The knowledge built up, generalised and rem em bered by the M aster, his greatest stock in trade, is totally lacking to the mechanical player. Such knowledge as the p ro g ra m s have is embedded in the plausibility analysis and the evaluation function; they cannot gen eralise and they cannot learn. It is generally agreed that the next step in computer chess is to find some way of building the chess M a s te r 's knowledge into a p rogram . The time when it was thought that a chess p ro g ra m m e r did not need to know anything about chess has long passed. N e a rly e v e r y team c om ­ peting at Stockholm had at least one good chess player attached to it: f o r example; D .Slate (CHESS 4 .0 ) is a strong Expert; G.Rajna ( P A P A ) and A . V . B it m a n (KAISSA) are both National M a s te rs . An unkind o b s e r ­ v e r might comment that a quarter of a century is a long time to pass before Shannon's words, written in 1950, are heeded: 'Even with the improvements we have discussed [ i . e . a variable depth of search and plausibility analysis] the above strategy gives the im pres-

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sion of relying too much on " b r u t e - fo r c e " calculations rather than on lo gical analysis of a position. It plays something like a beginner at chess who has been told some of the prin ciples and is p ossessed of tremendous energy and accuracy f o r calculation but has no exp erien ce with the game. A chess master, on the other hand, has available know­ ledge of hundreds o r perhaps thousands of standard situations, stock combinations and common manoeuvres which occur time and again in the game. T h e r e are f o r example, the typical s a c r ific e of a knight at B7 o r a bishop at R7, the standard mates such as the " P h il id o r le g a c y ", manoeuvres based on pins, forks, d is c o v e rie s , promotion, etc. In a given position he re co gn izes some s im ila rity to a f a m ilia r situation and this d irects his mental calculations along lines with g r e a t e r probability of success. 'T h e r e is no reason why a p rogram based on such "type positions" could not be constructed. This would require, however, a rather form idable analysis of the game.' Chess M asters, p r o g r a m m e r s and A r t i f i c i a l Intelligence scientists are now beginning to join fo r c e s . A recent s e r ie s of sem inars held at Northwestern University, home of CHESS 4.0, could be said to mark the o ffic ia l beginning of this tr i- p a r tite approach. At Northw estern it was agreed that the next, and main, task is to implement Shannon's points quoted above. L a b o ra to rie s at Carnegie M ellon U n iversity (Dr H . J . B e r l i n e r ) and at Edinburgh U n iversity ( P r o f . D .M ic h ie and Dr S . T . T a n ) w e re represented at Northwestern and have embarked on the task outlined there. The involvement of students of A r t ific ia l Intelligence a r is e s fro m their avowed aim to build a mechanical intelligent system . Chess is a deep and difficult game, the intellectual game par excellence . If a computer program could beat a M a s te r chess p la ye r it would be hard to deny the p rogram some v e r y real measure of intelligence, since we now know that it cannot be done by super calculating p ow ers. Some w o r k e r s are convinced that the breakthrough w ill happen within the next three years: some are even m ore strongly convinced that it w ill not. The Appendixes reco rd these opposing b e lie fs and also give an account of what it is like f o r a M a s te r to play chess against one of the best of the current p r o ­ gra m s at queen odds. CHESS AS SIN People often ask what is the point of computer chess. The immediate and honest answer is 'Fun'. It must be rem em b ered that chess has always exerted a powerful fascination on the minds of its devotees, and has som etim es brought down punishment—the Bishop of F lo re n c e played in public and had to wash the feet of twelve of the poor as a penance, while Savanarola consigned chess sets to the fla m e s a y e a r b efore he was burned him self. The follow ing extract fro m the notes of an unknown seventeenth-century p r ie s t,* when examining his conscience on the sub­ ject of chess, are interesting and moving: '1. It is a great time w a ster. How many precious hours (which can never be reca lled ) have I profusely spent in this game.

* F r o m the Harleyan Miscellany, in the lib ra ry of Edward H arley, fir s t e a rl of Oxford (cited by de Groot).

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2. It hath had with me a fascinating property: I have been bewitched by it; when I have begun I have not had the power to g iv e over. 3. It hath not done with me when I have done with it. It hath followed me into my study, into my pulpit; when I have been praying o r preaching, I have (in my thought) been playing at c h e s s . .. 4. It hath caused me to break many solemn resolutions; nay, vows and p r o m is e s . Som etim es I have obliged m yself, in the most solemn manner, but to play so many mates at a time, o r with any one person, and anon I have broken these obligations and p r o m i s e s . . . 5. It hath wounded my conscience and broken my peace. I have had sad reflection s upon it, when I have been most serious. I find, if I w e re now to die, the rem em brance of this game would greatly trouble me and stare me in the face. I have read in the life of the famous John Huss, how he was greatly troubled, fo r his using of this game, a little before his death. 6. My using of it hath occasioned much sin, as passion, strife, idle (if not lying) words, in m yself and my antagonist, o r both. It hath caused the neglect of many duties both to God and m e n . . . ' In modern tim e s we have a testimony from M r s Sonia Graf Stevenson— a strong woman player in the thirties and on two occasions the United States Woman Champion: 'What is a gam e of ch ess? It is hard work, struggle, renunciation, insomnia produced by the chaos of variations: it is joy, deep emotion, intimate and full vibration of our whole b e i n g . . . ' De Groot is a little s e v e r e with her: 'Somewhat less controlled in her reactions, and less r e s e rv e d in her expressions than most of her male c o lleagu es'! P r o g r a m m e r s are m ore reticent (o r less articulate) and so fa r no Dean of Science has consigned a chess program to the flames: but both Deans and p ro g ra m m e r s would testify that something of the same f e v e r that Savanarola strove to combat grip s those that work in computer chess. It is also maintained that the study of computer chess w ill have bene­ fits to cognitive psychology and the program m ing industry, and that if the problem of computer chess is cracked the process w ill be gen era­ lised to a wide range of p roblem s. T h e re is still discussion as to whether there is any point at all in trying to copy human chess-playing p r o c e s s e s . But fundamentally everyone in the field, whether in chess, cognitive psychology, program m ing o r a r tific ia l intelligence seems to a g ree with the words of the late H .O 'D . Alexander, International M aster and f o r m e r British champion: 'W ill this [the achievement of m aster play by computer] degrade chess and re m o ve its interest? I don't think so. It w ill affect our view of how the human mind works and what it is, but that is another and w ider issue with implications outside chess. It w ill not alter the beauty and fascination of a great human game, nor reduce the creative effort in­ volved any m ore than good computer music would devalue Beethoven. That an aeroplane can fly o v e r E ve re st does not alter the human triumph in climbing it. 'A real success— the production of great games and not just the a v o i­ dance of blunders—in the attempt to mechanize chess must at the very least teach us a good deal about the nature of thought.'

Bibliography A d e lso n -V e ls k ii, G .M , A r la z a r o v , V. L . Bitman, A . R, Zhivotovsku, A . A., Uskov, A. V. (1970) P ro g ra m m in g a computer to play chess. Uspekhi Matematicheskikh Nauk 15(2), 221-62. A d e lso n -V e ls k ii, G .M , A r la z a v o v , V. L, Donskoy, M. V. On some methods of chess play p rogram m in g (in preparation). Alexander, H .O 'D .(1 9 7 3 ) A book o f chess. New York: H arper and Row. Babbage, C. (1864) Passages fro m the life o f a philosopher. London: Longman, Green, Longman, R oberts and Green. Reprinted 1961 (eds. P . M o r r i s o n and E m ily M o r r is o n ) in Charles Babbage and his Cal­ culating engines. New York: D over Publications. Bergson, H. (1902) L 'e f f o r t intellectuel. Rev. Phil.de la France et de l 'etranger 73,1-27. Bernstein, A., Roberts, M .D e V., Arbuckle, T ., and B e l s k y , M . A . (1958) A chess playing program f o r the IBM 704. P r o c .1958 Western Joint Computer Conference 13, 157-9. B ie rc e , A . (1909) M oxon's M aster, in The Collected Works o f Ambrose B ierce. New York: Neale Publishing Co. B in e t,A . (1893) L e s grandes m e m o ir e s . Resume d ’une enquete sur les joueurs d 'e checs. Revue de deux mondes, 826-59. Binet, A . (1894) Psychologie des grands calculateurs et joueurs d 'echecs. P a ris : Hachette. Botvinnik, M . M . (1970) Computer chess and long-range planning. New York: Springer V e rla g . Good, I. J. (1968) A f i v e - y e a r plan f o r automatic chess, in Machine Intelligence 2 (e d s . E . D a le & D .M ic h ie ), 89-118. Edinburgh: O l i v e r & Boyd. Reprinted by Edinburgh U n iversity P r e s s , 1971. Graf, Sonja (1940) Asi juega una mujer. Buenos A ir e s : E d ito ria l Sudamericana. Greenblatt, R .D , Eastlake, D .E , and C ro c k e r S .D . (1967) The G reenblatt chess p ro g ra m . Proceedings o f the FJCC, 801-10. G re go ry, R . L . (1970) The intelligent eye. London: Weidenfeld and Nicolson. Groot, A . de (1965) Thought and choice in chess (ed G .W . B a y lo r). The Hague & P a ris : Mouton. (Translation, with additions, of Dutch v e r ­ sion of 1946). Harkness & Battell (1947) American Chess Review. Huberman, Barbara J. (1968) A program to play chess endgames. Ph.D. thesis, Stanford University. Hunter, I . M . L . (1962) An exceptional talent f o r calculative thinking. B rit. J. Psychol. 53, (3 ), 243-58. Jones, W. (1799). The works o f Sir William Jones, 4, 499-512. London: G .G .a n d J.Robinson, and R .H .E v a n s . K ister, J., Stein, P., Ulam, S., Walden, W., and W ells , M . (1957) E x p e r i­ ments in chess. J. Assn. Comput. Mach. 4, 174-7. Kotok, A. (1963) A chess playing program f o r the IB M 7090. B a ch elors thesis, Massachusetts Institute of Technology. Maynard-Smith, J.& Michie, D. (1961) Machines that play gam es. New Scientist 12, 367-9. M ichie, D. (1966) Game playing and game learning automata (with appendix by J.M aynard Smith), in Advances in programming and non-numerical computation, (ed L . F o x ) , 183-200. Oxford: P e r g a mon P r e s s . Michie, D. (1976) King and rook against king, in Advances in computer

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chess 1 (ed M. C lark e). Edinburgh: Edinburgh U n iversity P r e s s (in p r e s s ). Neumann, J. von, & M orgenstern, O. (1944) The theory o f games and economic behaviour. Princeton: Princeton University P r e s s . Newborn, M . (1972) The ACM 1972 computer chess booklet, D epart­ ment of E le c tr ic a l Engineering and Computer Science, Columbia U n iversity. N ew ell, A., Shaw, J. C, and Simon, H. A . (1958) Chess playing p rogram s and the problem of com plexity. IBM J .R es.D ev 2 , 320-35. Reprinted in Computers and thought ( e d s . E . A. Feigenbaum & J. Feldman), 3970. New Y o rk etc: M cGraw Hill, 1963. Samuel, A . L . (1959). Some studies in machine learning using the game of checkers. IBM J. Res. Dev. 3, 210-29. Samuel, A . L . (1967). Some studies in machine learning using the game of checkers II. Recent p ro gre ss . IBM J. Res. Dev. 11, 601-17. Shannon, C . E . (1950) P ro g ra m m in g a computer fo r playing chess. Phil. Mag. {London), 7th ser. 41, 256-75. T a n , S . T . (1972) Representation of knowledge f o r v e r y simple pawn endings in chess. Research Memorandum M IP-R -98 , Department of Machine Intelligence, Edinburgh U niversity. Tan, S . T . (1974) Kings, pawn and bishop. Research Memorandum M IP R-108, Department of Machine Intelligence, Edinburgh University. T a n , S . T . (1976) D escribin g pawn structures, in Advances in computer chess 1 (ed M. C lark e). Edinburgh: Edinburgh University P r e s s (in p re s s ). Turing, A . M . (1953) Digital computers applied to games. Faster than thought (ed B. V. Bowden), 286-310. London: Pitman. Vigneron, H. (1914) L e s Automates. La Nature, 56-61.

Plate 1. CHAOS struggling slowly towards victory, a rook and a pawn ahead, against CHESS 4.0. Left, D .Slate (CHESS 4.0); centre, seated, F. Swartz (CHAOS); right, V. Berman (CHAOS).

P la te 2. M .V .D o n s k o y (KAISSA) playing Black. His p ro gra m has just missed a mate in one.

P la te 3. A board position from game 2, with KAISSA playing White and F R A N T Z playing Black. David L e v y is predicting B lack’ s thirteenth m ove (see game record ).

P la te 4. Robert M axwell presenting the Gold Medal to M. V. Donskoy

Appendix 1 M A N A G A IN S T M ACH INE 1974 (Dr Hans B e rlin e r is an International Chess M a s te r and f o r m e r W orld Correspondence Chess Champion. He prep ared these notes at our r e ­ quest after playing CHESS 4 .0 (at queen odds) during a conference on computer chess held at Northwestern University, Evanston, Illin o is in N ovem b er 1974. Dr B e r l i n e r 's comments should be considered along with the te rm s of the w a ger printed as Appendix 2.) T o gain some appreciation of what it means to play a game o f chess with a handicap of a queen, I could best say that a chess m a ster would have hardly any expectation of beating a class 'D' player, fiv e catego­ r ie s below him in ranking, in such a gam e. In fact, such gam es are usually just played in clubs by strong p la y e rs against p la y e rs who a re so weak o r inexperienced that they have not made it to the rating scale as yet. The best chess p ro g ra m s a re now rated as solid c la s s C players, and on occasion even achieve a class B rating in a tournament. One might th e re fo re ask, how can a m aster conceive of giving queen odds to such a program (and CHESS 4 .0 is one of the best, if not the best)? The answer lie s in understanding the structure of chess p ro g ra m s . Current p ro g ra m s are v e r y good tactically (fo r their rating), but poor stra tegica lly. Thus they frequently cannot see what is coming until it is about to hit them. They also have another gla rin g weakness, the Horizon Effect, which is caused by the way their tr e e search is o r g a ­ nized. (See 'Some N e c e s s a ry Conditions f o r a M aster Chess P r o g r a m ', P ro ceed in gs of the 3rd International Conference on A r t i f i c i a l In te lli­ gence, Stanford University, August 1973). Given the p ro p er conditions, a p rogram may, because of the Horizon Effect, throw away p iece after piece in an apparently senseless (to a human o b s e r v e r ) e ffo rt to avoid a set of unavoidable consequences. Thus the procedure f o r playing a queen odds game against a p rogram is quite different to that which would be used against a human. In this game I w ill try to take advantage both o f the p r o g r a m 's minimal s tra te ­ gical understanding and of the Horizon E ffec t. The f ir s t task in the opening w ill be to try to get a position which has a 'c lo s e d ' character so that the extra m aterial cannot be easily put to work by the p ro g ra m . We w ill also try to avoid exchanges, which on the other hand the p r o ­ gram w ill e a g e rly try to prom ote. White: H . B e r l i n e r

Black: CHESS 4 .0

15 N ovem b er 1974 (White gave odds of queen) 1 2

P-Q4 B-B4

P-Q4

T h is and many subsequent moves are directed against a possible P -K 4 by Black which would open up the game too much. I now expected B-B4 since the Q B P would be awkward to defend, and moving it would allow B x N which swaps down. However, I had intended to meet that with 3 N-QB3 B x p 4 R-QB1 B-B4 5 N-N 5 with a good game. 2 3

... P-Q B3

N-QB3 P -K N 3

Appendix 1 4 5

P -K 3 B-N3

(101

B-R3

Naturally we avoid a swap. 5 6 7

... N-B 3 B-N5

N-B3 B-N5

T h e r e was nothing sensible that could be done about B lack 's intended BxN. 7

...

N-K5

Black is in no hurry. Now 8 N -K 5 is not good because the obvious B-Q2 m eets all threats. My next move is a fine move which threatens P-B 3 winning a piece, because if N x B then R P x N and both Black bishops are attacked and cannot both be saved. However, the threat is mainly bluff and would be successful except that Black overlooks the threat as the principal variation is too deep. Then I dare not win the piece on move 9 because of 9 B x N ch P x B 10 P -B 3 N x B 11 P x N Bx K P 12 P x B and W h ite’ s position is in ruins. 8 9

N -N 1 B-Q3

P -R 3 B-B4 (!)

With this fine move which threatens mayhem with N x B , Black has d efi­ nitely won the opening and White must now regroup, acquiescing to the exchange of two sets of pieces, and see what he can make of things. 10 11 12

B-K2 RPxN QRx B

Nx B BxN

I considered taking the other bishop, but W hite's main hope here is that Black w ill castle on the king's side where it is possible to get an attack, and I was afraid that a rook at R6 might show up in the evaluation func­ tion somewhere and inhibit castling. 12 13

... P -K B 4

B-N2

Must ’p rev e n t’ P - K 4 . 13 14 15

... P -K N 4 K-Q2

Q-Q2 0-0

(Hurrah!)

The beginning of an intricate plan to trap the black queen. F ir s t the white king must get out of the way to unite the rooks, and keep the bishop protected. Knowing something about CHESS 4 . 0 ’ s evaluation function, I also thought this might lure some pieces to the queen's side f o r an attack on the king. 15 16 17

... P-Q N3 N-B3

N-R4 QR-B1

The trap has been baited, and it would seem almost impossible fo r any p rogram to refuse to 'win' a pawn here. Of course, the fact that the queen gets into v e r y restricted circumstances is not noticed. 17 18

... N-N5

QxP QxNP

Appendix 1

102)

Q-Q2 avoids 'winning' the pawn, but White would get a strong attack then, 19

NxRP

Here it was already possible to get a perpetual attack on the queen by QR-KN1, Q-B7, R-KB1, etc., however, I did not like the thought of Black giving up the queen and then having a rook and two pawns in compensa­ tion, which would be too much. In such positions one can be absolutely sure that the p rogram w ill move the rook away, allowing time f o r the knight to return, because the whole problem of the perpetual attack on the queen has not been noticed. 19 20 21 22

... N -N 5 QR-KN1 N-R3

KR-Q1 P-QB4 Q-B7

T h is is the c r itic a l point in the game. Black should now be becoming aware of the problem with his queen. T h is is a m u lti-fold situation which is v e r y difficult to predict from my point of view . W ill Black blissfully play the queen back and forth until an actual repetition is at hand and then give up the queen in o r d e r to avoid the draw, since it is still m a terial ahead? W ill Black see the problem and give up the queen fo r rook right away (as it did)? O r w ill Black seek to postpone the in ­ evitable, when it becomes noticed, by the s a c r ific e N x P ch, which would be the Horizon Effect at its best. I was in an isolated room, but Dave Slate, one of the p ro g ra m m e r s of CHESS 4.0, was demonstrating these p ossib ilities to the watching audience. It turned out that the fateful d e c i­ sion was made because the p rogram had saved up enough tim e from its previous moves to go to depth 6. At depth 5 it would have played N x P c h and then I would have been happy. A s it was, I wonder whether 22 R-KB1, which is le ss fo rcin g but just as e ffective, would have caused the program to spend m ore time so that it couldn't go to depth 6 later. At the time, my only thought was to get the p rogram to reco gn ize the problem now, so that it would make an inappropriate response. But it didn't work out that way. 22 ... Q-R5 23 N-N 5 QxR 24 RxQ P-N4 Now there was still some scant hope that the p ro gra m would not be able to win this position against resistance which would not help it in any way, o r that it could be side-tracked somehow. However, neither of these p ossibilities m a terialized, it played the end game in excellent fashion. 25 26 27 28 29 30 31 32

B-N4 B-B3 B-K2 BPx P B-Q3 R-KN1 N-B3 R-KR1

P-B4 R-Q3 PxP R/3-QB3 P -N 5 B-B3 K-B 2

N -K 5 would now and later be met by B x N which only s im p lifie s B lack 's task. 32

...

R-KR1

Appendix 1 33 34 35 36 37 38 39 40 41 42

R-KN1 R-N 2 N -K 1 B-B2 N-Q3 B -N 1 NxP NxP/6 N-N4 N-Q3

P -K 3 R-R8 K -N 2 R -B 6 R -R 6 N-N 2 R/R6x P BxP R-B 6 N-B4

(103

White resigns

It was getting late and I thought the audience might be getting impa­ tient. W h ite's game is hopeless, of course, but in a game fo r stakes I would have played a little longer. A v e ry interesting encounter; CHESS 4 .0 played the opening and ending v e r y w e ll and had enough when it counted in the middle game.

Appendix 2 (Reprinted fro m Firbush News 5)

C O M P U T E R CHESS C H A L L E N G E 1978 In August 1968, M r David L e v y o ffe re d a bet that no computer p rogram would beat him at chess a c ro s s the board f o r the next ten y e a r s . At that time, M r L e v y was Scottish Chess Champion with a rating of approxim ately 2250: he is now an International M aster, with a rating of 2320. The bet was accepted by P r o f e s s o r J .M c C a rth y and P r o f e s s o r D. M ichie at £250 each, even odds. In 1970 P r o f e s s o r S. P ap ert joined the consortium and in 1971 P r o fe s s o r E. K ozd row ick i followed suit, each of the two new m em b ers of the consortium staking £250. It now seem s tim e to fo r m a liz e the basic te rm s of the wager, and we are pleased to print the f ir s t draft here. M r David L e v y ' s w a ger with the consortium states that he w ill not be beaten in a chess match a c ro s s the board by any computer p rogram before 31 August 1978. The following rules w ill apply: O R G A N IZ A T IO N O F M A T C H E S 1.

A match shall consist of an even number of games, less than or equal to ten, at the choice of the challenger.

2.

A challenge to such a match may be issued at any tim e by any m e m b e r(s ) of the consortium, the ch a llen ger(s) being responsible f o r the organization and funding of the p la y -o ff.

3.

No lim it is set to the number of such challenges which may be issued before 31 August 1978.

4.

M r David L e v y may not postpone his answer to a challenge fo r m ore than two weeks.

5.

In the event of the death of any m em ber of the consortium before 31 August 1978, that m e m b e r 's bet shall be cancelled. In the event of the death o r lasting incapacity of M r David L e v y b efo re 31 August 1978, all bets are off.

G E N E R A L RULES O F P L A Y 1.

The rules governing human international tournament play w ill be followed where applicable, but there w ill be no adjournments.

2.

T h e r e are no restrictio n s on hardware fa c ilitie s , but no allowance w ill be made f o r technical d ifficu lties (machine failure, p rogram failure, communication failu re o r e r r o r ) .

3.

An inspector nominated by M r L e v y w ill remain at the computer site while a match is being held. In the case of a geographically distributed system, methods of policing may be agreed ad hoc between the m em b ers of the consortium and M r L e v y .

4.

Detailed rules of play w ill be agreed between M r L e v y and the challenging m em b ers of the consortium before any challenge match is arranged, and these rules w ill be made public.

5.

T h e r e is no bar to M r L e v y making any number of s im ila r w a g e rs with other persons.

Appendix 2

(105

6.

Should M r L e v y act as computer chess consultant to any m em ber of the consortium, he does so at his own risk, but is f r e e to seek a renegotiation of te rm s as under 7 below.

7.

Any m em b er of the consortium is f r e e to abrogate o r adjust the te r m s of his w a g e r by agreement with M r L e v y .

At the time of this issue going to p ress, (October 1974) P r o f e s s o r M ichie has increased his w a ger with M r L e v y to a stake of £500 and has laid a second w ager with M r L e v y (wager accepted) that if M r Levy lo s e s his bet it w ill be through defeat by a p rogram developed under P r o f e s s o r M ic h ie 's direction. The amount of the second w a ger is also £500, so that P r o f e s s o r Michie has now a total of £1,000 at stake and M r L e v y a total of £1, 750.