Astounding Blunder

[Mincho Georgiev]

This goes on top of my priority list.
Accidentally i observed this game today.

[Event "ICS rated standard match"]
[Site "freechess.org"]
[Date "2010.03.28"]
[Round "?"]
[White "GnuCheese"]
[Black "PawnyX"]
[Result "1/2-1/2"]
[WhiteElo "2298"]
[BlackElo "2325"]
[PlyCount "169"]
[EventDate "2010.??.??"]

1. c4 Nf6 2. d4 e6 3. Nf3 Bb4+ 4. Bd2 Bxd2+ 5. Qxd2 d5 6. Nc3 O-O 7. e3 Qe7 8.
cxd5 exd5 9. Bd3 Nc6 10. O-O Bg4 11. Be2 Ne4 12. Nxe4 dxe4 13. Ne1 Be6 14. f3
Bd5 15. fxe4 Bxe4 16. Bf3 Rad8 17. Nd3 Rfe8 18. Rac1 Bxf3 19. Rxf3 Rd6 20. Rcf1
f6 21. Qc2 b6 22. b4 Nd8 23. Qa4 c6 24. Nf2 Kh8 25. Nd1 Ne6 26. Qb3 Ng5 27. Rf4
Ne4 28. Qc2 Qe6 29. a4 Kg8 30. Qd3 Rd7 31. Kh1 Rde7 32. Qc2 Qd6 33. Rf5 g6 34.
R5f4 Re6 35. Qa2 Qd5 36. Qb2 f5 37. R4f3 Qc4 38. Kg1 Nf6 39. Qa3 Nd5 40. b5
cxb5 41. axb5 R6e7 42. Qa1 Qxb5 43. Nc3 Nxc3 44. Qxc3 Qd5 45. Rc1 Re6 46. Rc2
R8e7 47. Qd3 Kf7 48. Rcf2 Ke8 49. Rc2 Rc6 50. Rxc6 Qxc6 51. Rf1 Kd8 52. Rb1 Qe4
53. Qxe4 Rxe4 54. Kf2 f4 55. Kf3 Rxe3+ 56. Kxf4 Re2 57. Rg1 Kc7 58. Kf3 Re8 59.
g3 Kd6 60. Rc1 g5 61. Kg4 h6 62. Kf5 Re2 63. Ra1 a5 64. Rb1 Kc7 65. Rc1+ Kd7
66. Rb1 Kc6 67. Rc1+ Kd5 68. Rb1 Rf2+ 69. Kg6 Kxd4 70. Kxh6 Rxh2+ 71. Kxg5 Kc5
72. Rc1+ Kb5 73. g4 a4 74. Kf4 a3 75. g5 Rg2 76. Rb1+


[D]8/8/1p6/1k4P1/5K2/p7/6r1/1R6 b - - 0 76


76...Ka4?? 77. Rxb6 a2 78. Ra6+
Kb3 79. Kf5 Rf2+ 80. Ke6 Rc2 81. Rxa2 Rxa2 82. g6 Rd2 83. g7 Rg2 84. Kf7 Rxg7+
85. Kxg7 1/2-1/2

[metax]

After Ka4 the draw seems easy to see even for weak engines like ChessMind (which doesn't play Ka4 at any iteration in the start position):

8/8/1p6/6P1/k4K2/p7/6r1/1R6 w - -

Engine: ChessMind 0.72 (0 MB)
by metax

7.00 0:01 -0.12 1.Rxb6 a2 2.Ra6+ Kb3 3.Rb6+ Kc4
4.Ra6 Re2 5.g6 Kb5 6.g7 Rf2+ (512.511) 296

8.00 0:03 -0.15 1.Rxb6 a2 2.Ra6+ Kb5 3.Ra7 Rf2+
4.Ke3 Kb6 5.Ra8 Rc2 6.g6 Rc3+ (1.133.276) 307

9.01 0:06 -0.13 1.Rxb6 a2 2.Ra6+ Kb5 3.Ra7 Rf2+
4.Ke4 Kb6 5.Ra3 Kc5 6.Rc3+ Kb4 7.Rc1 Re2+ (2.004.218) 316

best move: Rb1xb6 time: 0:08.939 min n/s: 320.000 nodes: 2.520.053

[Mincho Georgiev]

Exactly. It's most likely a nasty bug or needs draw recognition code in such cases if the search cannot solve it alone.
Thanks for the input.

[metax]

Well, the shocking thing is:

8/8/1p6/6P1/k4K2/p7/6r1/1R6 w - -

Engine: Rybka 2.2n2 (128 MB)
by Vasik Rajlich

15.01 0:01 -4.00 1.Ra1 b5 2.Kf3 Rxg5 3.Kf4 Rg6 4.Kf5 Rg2
5.Kf4 a2 6.Kf3 Rb2 7.Ke3 Kb3 (317.920) 242

16.01 0:02 -4.28 1.Ra1 b5 2.Kf3 Rxg5 3.Kf4 Rg6 4.Kf5 Rg2
5.Kf4 a2 6.Kf3 Rb2 7.Kf4 Kb3 (599.685) 271

17.01 0:04 -5.94 1.Ra1 b5 2.Kf3 Rxg5 3.Kf4 Rg6 4.Re1 a2
5.Ke5 Rg2 6.Kd6 b4 7.Kd5 Kb3 (1.318.941) 279

17.03 0:09 -1.74 1.Rxb6 a2 2.Ra6+ (2.125.521) 238

18.01 0:09 -1.74 1.Rxb6 a2 2.Ra6+ (2.147.557) 236

19.01 0:23 -0.06 1.Rxb6 a2 2.Ra6+ (4.393.751) 190

20.01 0:24 -0.06 1.Rxb6 a2 2.Ra6+ (4.435.031) 188

21.01 0:27 -0.06 1.Rxb6 a2 2.Ra6+ (4.850.940) 183

best move: Rb1xb6 time: 0:31.216 min n/s: 5.493.367 nodes: 5.493.367

8/8/1p6/6P1/k4K2/p7/6r1/1R6 w - -

Engine: ProDeo 1.5 (0 MB)
by Ed Schroeder

12.00 0:01 -2.39 1.Rxb6 a2 2.Ra6+ Kb3 3.Kf5 Rg1 4.g6 Ra1
5.Kf6 (2.856.428) 2856

13.01 0:02 -2.17 1.Rxb6 a2 2.Ra6+ Kb3 3.Kf5 Kb2
4.Rb6+ Kc2 5.Ra6 Kb1 6.Kf6 Ka1 7.Kg6 Kb2
8.Kh7 (5.817.317) 2908

14.01 0:14 -1.54 1.Rxb6 a2 2.Ra6+ Kb3 3.Ra8 Rf2+
4.Ke4 Kc4 5.g6 Re2+ 6.Kf5 Rf2+ 7.Ke4 Re2+
8.Kf5 Rf2+ (28.751.584) 2053

best move: Rb1xb6 time: 0:43.711 min n/s: 2.053.684 nodes: 28.751.584

8/8/1p6/6P1/k4K2/p7/6r1/1R6 w - -

Engine: Twisted Logic 20100131x (128 MB)
by Edsel Apostol, Philippines

12/27 0:01 -2.90 1.Rxb6 a2 2.Ra6+ Kb3 3.Kf5 Rg1 4.g6 a1Q
5.Rxa1 Rxa1 6.g7 Ra8 7.Kg6 Kc4 8.Kh7 Ra7 (1.193.801) 736

13/30 0:03 -2.37 1.Rxb6 a2 2.Ra6+ Kb3 3.Kf5 Kb2
4.Rb6+ Kc2 5.Ra6 Kb1 6.g6 a1Q
7.Rxa1+ Kxa1 8.Kf6 Kb2 9.g7 Kc3
10.Kf7 Rf2+ 11.Ke6 (2.866.271) 833

14/32 0:07 -1.21 1.Rxb6 a2 2.Ra6+ Kb3 3.Kf5 Rf2+
4.Ke6 Rc2 5.g6 Rc6+ 6.Rxc6 a1Q 7.Rc7 Qe1+
8.Kf7 Qf1+ 9.Ke6 Qe2+ 10.Kf7 Qf3+
11.Kg7 Qd5 12.Rc1 Qd4+ 13.Kf7 (6.437.839) 894

15/32 0:10 -1.22 1.Rxb6 a2 2.Ra6+ Kb3 3.Kf5 Rf2+
4.Ke6 Rc2 5.g6 Rc6+ 6.Rxc6 a1Q 7.Rc7 Qe1+
8.Kf7 Qf2+ 9.Ke8 Qe2+ 10.Re7 Qb5+
11.Kf7 Qf5+ 12.Kg7 Kc4 13.Rc7+ Kd4 (9.784.189) 903

16/34 0:21 -0.88 1.Rxb6 a2 2.Ra6+ Kb3 3.Kf5 Rf2+
4.Ke5 Re2+ 5.Kf5 Re1 6.g6 a1Q 7.Rxa1 Rxa1
8.g7 Rg1 9.Kf6 Kc4 10.Kf7 Kd5 11.g8Q Rxg8
12.Kxg8 (20.430.783) 956

17/35 0:37 -0.82 1.Rxb6 a2 2.Ra6+ Kb3 3.Kf5 Rf2+
4.Ke5 Re2+ 5.Kf5 Rc2 6.g6 Rc7 7.Rb6+ Kc2
8.Ra6 Kb1 9.Kf6 Rc6+ 10.Rxc6 a1Q+
11.Ke6 Qa2+ 12.Kf6 Qb2+ 13.Ke6 Qb3+
14.Ke7 (37.599.368) 1008

best move: Rb1xb6 time: 0:43.867 min n/s: 1.001.889 nodes: 43.687.375

23 seconds for Rybka, the others don't even find it (and there are some more engines that do not find it very quickly) but Stockfish and my extremely weak engine find it in 0 seconds... Strange...

[Mincho Georgiev]