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A tale of human error as a computer finds the win that a grandmaster missed.

White: L Ljubojevic Black: V Anand Buenos Aires 1994 1. e4 c5 2. Nf3 d6 3. d4 cxd4 4. Nxd4 Nf6 5. Nc3 Nc6 6. Bc4 e6 7. Be3 a6 8.

Bb3 Qc7 Black's last two moves are designed for quick counterplay if White continues with Qe2 and 0- 0-0. Instead Ljubojevic adopts an older plan with K-side castling.

9. f4 Be7 10. Qf3 Nxd4 11. Bxd4 b5 12. a3 12. e5 is simply met by Bb7.

12 . . . 0-0 13. 0-0 Bb7 14. Ra1 Rac8 15. Qg3 Kh8 16. Kh1 Qc6 17. Rf3 a5 18.


Putting the queen on the same diagonal as Black's bishop looks curious, but this is an effective way to increase the pressure.

18 . . . b4 19. axb4 axb4 20. Nd1 h6 21. Rh3 Kh7 Necessary to avoid the threat of a mating attack with Rxh6+.

22. Nf2 Rg8 With Ng4 coming, Black must defend g7.

23. Ng4 Nxg4 24. Qxe7] Better than the routine recapture on g4. Now both Qxf7 and Qh4 are threatened.

24 . . . e5 25. fxe5 dxe5 26. Bg1 Nf6 Now 27. Bxf7 Rfd8 is unclear. Instead Ljubojevic opens the position still further.

27. Qxe5 Nxe4 28. Qf5+ Kh8 29. Bd4 (see diagram) Black's game looks (and is) desperate. The immediate threat is 30. Rxe4 Qxe4 31. Rxh6 mate. Another version of the same idea is 30. Bd5 Qxd5 31. Rxh6 mate. Though any black knight move would threaten mate, there is no useful way to do it: Nf2+ or Ng3+ lose to Qxf2 and Rxg3; Nd6 allows instant mate and Nf6 loses to Rxh6+ with Bxf6+ to follow.

29 . . . Rcd8] The only defence. Now 30. Rxe4 is met by Rxd4] while the clever 30. Bd5 fails to 30 . . . Rxd5 31. Qxd5 Nf2+]] 30. c3 Nd2 31. Qg5??

It didn't work last move, so White forgets to look at it this time, but 31.

Bd5] would have won at once. 31 . . . Rxd5 loses to 32. Qxd5 Qxd5 33. Rxh6 mate. The first to spot this was the computer program Chess Genius - but machines' thought processes are rarely bothered by what they were thinking about on the previous move.

31 . . . Rxd4 32. cxd4 Nxb3 33. d5 Re8] Is this what White overlooked? Instead 33 . . . Qd6 loses to 34. Re6] 34. Rxe8+ Qxe8 35. Qe3 Qa8] 36. Rxh6+ A miscalculation in time-trouble, but with Bxd5 coming, White is struggling.

36 . . . gxh6 37. Qxh6+ Kg8 38. Qg5+ Kf8 39. Qh6+ Ke8 White resigns.

(Graphic omitted)