Los Alamos chess (or anti-clerical chess[1]) is a chess variant played on a 6×6 board without bishops. This was the first chess-like game played by a computer program. This program was written at Los Alamos Scientific Laboratory by Paul Stein and Mark Wells for the computer[2] in 1956. The reduction of the board size and the number of pieces from standard chess was due to the very limited capacity of computers at the time. The computer still needed about 20 minutes between moves.
The program was very simple, containing only about 600 instructions. It was mostly a minimax tree search and could look four plies ahead. For scoring the board at the end of the four-ply lookahead, it estimates a score for material and a score for mobility, then adds them. Pseudocode for the chess program is described in Figure 11.4 of Newell, 2019.[3] In 1958, a revised version was written for MANIAC II for full 8×8 chess, though its pseudocode was never published. There is a record of a single game by it, circa November 1958 (Table 11.2 of Newell, 2019).
The starting position is illustrated. All rules are as in chess except:
The computer played three games. The first was played against itself. The second one was against a strong human player, who played without a queen. The human player won. In the third game, MANIAC I played against a laboratory assistant who had been taught the rules of chess in the preceding week specifically for the game. The computer won, marking the first time that a computer had beaten a human player in a chess-like game.[2] [4]
White: Martin Kruskal Black: MANIAC I
1. d3 Na4 2. b3 Nb6 3. c3 d4 4. c4 bxc4 5. dxc4 a4 6. Na3 e4 7. Kd2 Ke5 8. f3 e3+ 9. Kc2 axb3+ 10. axb3 Nf4 11. Nd3+ Nxd3 12. Kxd3 Kf4 13. Kc2 Ra5 14. Kb2 Re6 15. Rfd1 Re5 16. Nc2 Rxa1 17. Kxa1 Re6 18. Kb2 Re5 19. Ne1 Qe4 20. fxe4 fxe4 21. Kc2 d3+ 22. exd3 e2 23. Ra1 Re6 24. Ra5 exd3+ 25. Kd2 Re4 26. Rxc5 Re6 27. Nxd3+ Ke4 28. Kxe2 Kd4+ 29. Re5 Rxe5+ 30. Nxe5 Kc5 31. Kd3 Kb4 32. Kd4 Nxc4 33. bxc4 Kb3 34. c5 Kb4 35. c6=Q Kb3 36. Nd3 Ka2 37. Qc3 Kb1 38. Qb2 [5]
White: MANIAC I Black: Beginner
1.d3 b4 2.Nf3 d4 3.b3 e4 4.Ne1 a4 5.bxa4 Nxa4 6.Kd2 Nc3 7.Nxc3 bxc3+ 8.Kd1 f4 9.a3 Rb6 10.a4 Ra6 11.a5 Kd5 12.Qa3 Qb5 13.Qa2+ Ke5 14.Rb1 Rxa5 15.Rxb5 Rxa2 16.Rb1 Ra5 17.f3 Ra4 18.fxe4 c4 19.Nf3+ Kd6 20.e5+ Kd5 21.exf6=Q Nc5 22.Qxd4+ Kc6 23.Ne5 [2]
. David Pritchard (chess player) . The Encyclopedia of Chess Variants . Games & Puzzles Publications . 1994 . Los Alamos Chess . 175–76 . 0-9524142-0-1.
. David Pritchard (chess player) . Beasley . John . The Classified Encyclopedia of Chess Variants . John Beasley . 2007 . Los Alamos Chess . 112 . 978-0-9555168-0-1.