ambiguous san: 'Nec3' in 8/8/6K1/4k3/4N3/p4r2/N3N3/8 w - - 3 82

[robertnurnberg]

This game was part of a pgn created by fastchess on fishtest. I assume the culprit is in chess-library.

[Event "Batch 44: new406 vs master"]
[Site "https://tests.stockfishchess.org/tests/view/678d48cfd63764e34db495ed"]
[Date "2025.01.19"]
[Round "144"]
[White "New-165e664d57c4dfde814377b58789b395b00f6751"]
[Black "Base-8e3e22b3d4f214e12aa83771be543aac1196d713"]
[Result "1/2-1/2"]
[SetUp "1"]
[FEN "r3k1nr/pbppqpb1/1pn1p2p/6p1/2PP4/2NBPN2/PP3PPP/R1BQ1RK1 w kq - 6 9"]
[GameDuration "00:02:37"]
[GameStartTime "2025-01-19T20:11:22 +0100"]
[GameEndTime "2025-01-19T20:14:00 +0100"]
[PlyCount "158"]
[Termination "adjudication"]
[TimeControl "45.161+0.452"]

1. Nb5 {+1.08/25 5.572s} d5 {-1.04/23 2.355s} 2. cxd5 {+0.99/21 1.442s}
exd5 {-1.06/21 1.189s} 3. Bd2 {+1.06/19 0.662s} a6 {-0.98/21 1.044s}
4. Nc3 {+1.03/20 0.690s} g4 {-1.09/22 2.064s} 5. Ne1 {+1.01/20 0.808s}
Nf6 {-1.03/20 0.702s} 6. Nc2 {+1.18/24 4.363s} h5 {-0.99/17 0.750s}
7. f3 {+1.27/20 0.662s} gxf3 {-1.08/23 3.331s} 8. Rxf3 {+1.43/22 2.222s}
O-O-O {-1.26/26 4.887s} 9. Qe2 {+1.28/21 1.703s} a5 {-1.33/23 1.452s}
10. Raf1 {+1.27/21 0.739s} h4 {-1.39/22 1.453s} 11. Be1 {+1.33/20 0.864s}
Kb8 {-1.21/23 5.064s} 12. a3 {+1.34/22 2.873s} Rdg8 {-1.26/22 1.168s}
13. Rh3 {+1.40/17 0.531s} Ne4 {-1.21/21 1.980s} 14. Nxd5 {+1.39/19 0.833s}
Qe8 {-1.34/21 1.086s} 15. Nc3 {+1.23/20 2.153s} Nd6 {-1.25/19 0.658s}
16. Rf4 {+1.31/19 0.708s} f5 {-1.23/19 0.683s} 17. Rfxh4 {+1.34/22 1.104s}
Rxh4 {-1.26/19 0.577s} 18. Bxh4 {+1.28/20 1.145s} f4 {-1.27/19 0.649s}
19. Bf2 {+1.26/18 0.784s} Qd7 {-1.18/20 0.904s} 20. Rh7 {+1.55/19 0.744s}
fxe3 {-1.15/18 1.427s} 21. Qxe3 {+1.55/20 1.433s} Ne7 {-1.22/19 0.718s}
22. Qf4 {+1.14/25 4.134s} Rf8 {-1.14/20 1.288s} 23. Qg3 {+1.16/24 3.201s}
Ndf5 {-1.01/23 4.085s} 24. Qg4 {+1.10/20 3.016s} Qe6 {-0.96/18 0.445s}
25. Be4 {+1.14/22 2.399s} Qg8 {-0.96/20 1.492s} 26. Rh3 {+1.12/17 0.460s}
Bc8 {-0.86/18 0.989s} 27. Rf3 {+1.30/19 0.632s} Rf6 {-0.14/19 0.729s}
28. Rd3 {+0.09/26 8.138s} Nd6 {-0.10/23 3.655s} 29. Qd1 {+0.11/17 0.672s}
Nxe4 {-0.13/20 0.641s} 30. Nxe4 {+0.29/18 0.361s} Rf8 {-0.09/23 1.899s}
31. d5 {+0.24/23 0.600s} Nxd5 {-0.07/19 0.334s} 32. Rxd5 {+0.19/21 0.553s}
Bb7 {-0.07/22 0.682s} 33. Ne3 {+0.20/25 0.490s} Bxd5 {-0.05/21 0.470s}
34. Qxd5 {+0.18/22 0.437s} Qxd5 {-0.06/21 0.631s} 35. Nxd5 {+0.10/21 0.734s}
Bxb2 {-0.09/21 0.698s} 36. a4 {+0.08/26 0.538s} b5 {-0.15/24 1.491s}
37. axb5 {+0.13/23 0.348s} a4 {-0.22/20 0.620s} 38. Ndc3 {+0.14/23 0.795s}
a3 {-0.12/22 0.651s} 39. Na2 {+0.13/20 0.291s} Be5 {-0.13/23 0.721s}
40. h4 {+0.05/26 1.982s} Rf4 {-0.08/29 0.739s} 41. Nec3 {+0.05/20 0.170s}
Rf5 {-0.08/22 0.641s} 42. Nb1 {0.00/24 1.351s} Bd6 {-0.05/23 0.644s}
43. Nbc3 {0.00/18 0.140s} Be5 {-0.04/21 0.464s} 44. g4 {0.00/25 0.205s}
Rf4 {0.00/33 0.688s} 45. g5 {0.00/25 0.245s} Bd4 {0.00/31 0.484s}
46. Bxd4 {0.00/25 0.180s} Rxd4 {0.00/33 0.498s} 47. Kg2 {0.00/30 0.280s}
Rxh4 {0.00/33 0.455s} 48. Kf3 {0.00/32 0.317s} Kb7 {0.00/40 0.692s}
49. Ne2 {0.00/32 0.496s} Rh8 {0.00/39 2.128s} 50. Kg4 {-0.03/23 0.875s}
c6 {0.00/29 0.355s} 51. b6 {0.00/28 0.304s} Rh2 {0.00/42 0.592s}
52. Nec3 {0.00/39 0.295s} Rg2+ {0.00/48 0.557s} 53. Kf5 {0.00/51 0.382s}
Rf2+ {0.00/40 0.778s} 54. Ke6 {0.00/45 0.398s} Rg2 {0.00/52 0.544s}
55. Kf6 {0.00/57 0.390s} Rf2+ {0.00/46 0.496s} 56. Ke6 {0.00/51 1.439s}
Rg2 {0.00/48 0.606s} 57. Kf6 {0.00/55 0.387s} Rf2+ {0.00/49 0.954s}
58. Kg7 {0.00/36 0.212s} Kxb6 {0.00/24 0.281s} 59. g6 {0.00/23 0.166s}
Kc7 {0.00/30 0.339s} 60. Kh6 {0.00/31 0.270s} Rh2+ {0.00/34 0.443s}
61. Kg5 {0.00/24 0.203s} Kd7 {0.00/39 0.448s} 62. g7 {0.00/25 0.214s}
Rg2+ {0.00/38 0.471s} 63. Kf6 {0.00/36 0.355s} Rf2+ {0.00/43 0.457s}
64. Kg5 {0.00/45 0.731s} Ke7 {0.00/32 1.647s} 65. g8=N+ {+0.08/19 0.321s}
Ke6 {0.00/27 0.237s} 66. Nh6 {+0.06/18 0.295s} c5 {0.00/26 0.472s}
67. Ng4 {0.00/26 0.384s} Rf5+ {0.00/32 0.490s} 68. Kg6 {0.00/25 0.631s}
Rf3 {0.00/27 0.333s} 69. Ne2 {0.00/24 0.356s} Kd5 {0.00/23 0.293s}
70. Nf6+ {0.00/27 0.389s} Ke5 {0.00/24 0.497s} 71. Nd7+ {-0.01/25 0.916s}
Ke6 {0.00/29 0.563s} 72. Nxc5+ {0.00/23 0.149s} Kd6 {0.00/26 0.575s}
73. Ne4+ {0.00/29 0.497s} Ke5 {0.00/32 0.371s} 74. Nec3 {0.00/31 0.604s}
Rf1 {0.00/26 0.358s} 75. Kh5 {0.00/29 0.377s} Rf3 {0.00/32 0.419s}
76. Nb5 {0.00/29 0.397s} Re3 {0.00/41 0.360s} 77. Nbc3 {0.00/29 0.465s}
Kf5 {0.00/41 0.360s} 78. Nd4+ {0.00/33 0.356s} Ke5 {0.00/38 0.681s}
79. Ndb5 {0.00/36 0.385s} Kf5 {0.00/36 0.861s, Draw by adjudication} 1/2-1/2

Parsing this pgn with python-chess gives this error:

  File "/usr/local/lib/python3.10/dist-packages/chess/pgn.py", line 1685, in read_game
    move = visitor.parse_san(board_stack[-1], token)
  File "/usr/local/lib/python3.10/dist-packages/chess/pgn.py", line 1059, in parse_san
    return board.parse_san(san)
  File "/usr/local/lib/python3.10/dist-packages/chess/__init__.py", line 3057, in parse_san
    raise AmbiguousMoveError(f"ambiguous san: {san!r} in {self.fen()}")
chess.AmbiguousMoveError: ambiguous san: 'Nec3' in 8/8/6K1/4k3/4N3/p4r2/N3N3/8 w - - 3 82
  Original source of game 1 has error ambiguous san: 'Nec3' in 8/8/6K1/4k3/4N3/p4r2/N3N3/8 w - - 3 82.

[robertnurnberg]

I guess once fixed the following FEN could be a useful test case, with checks whether each knight moving to c3 is encoded correctly in SAN: 8/8/6K1/4k3/N3N3/p4r2/N3N3/8 w - - 3 82. (Together with the original FEN with just 3 knights possibly moving to c3).

[robertnurnberg]

This seems to be a duplicate of #140 and so is probably fixed by #141. But adding more tests (also for other pieces) might be a good idea.