A Chess Puzzle in Reverse

Here with a quick chess puzzle one of my friends gave me.

The puzzle is a bit interesting; it is White to move and not mate in 1, which is the reverse objective of the usual puzzle (hence the title). The puzzle is a legal position from the starting position. I also have a few hints, given to me by the same friend:

Hint 1:

check the tags, it's not just a chess puzzle

Hint 2:

Without changing the position of the pieces, how would it be possible for White to make a legal move that isn't checkmate?

Well, I... messed up the FEN. There shouldn't be a white pawn on a6 (or h3 with the intended answer). Now it's possible. I think.

• Is the part about only having FEN part of the puzzle? If not, I can edit in a chess board real quick. – Quintec Oct 1 '18 at 16:19
• It would be fine with a board in, I honestly couldn't figure out how to put one in. – Excited Raichu Oct 1 '18 at 16:21
• According to the comments on the accepted answer, it would seem this puzzle has no solution. – Shufflepants Oct 1 '18 at 18:11
• @ExcitedRaichu Your edit makes it even worse. White is now missing 8 pieces and only 7 pawns need to make captures. Actually it's probably still 8 captures, but the reasoning doesn't work anymore. – Sleafar Oct 1 '18 at 18:37
• This style of chess puzzle, where you must reason about the past rather than the future, is called a "retro" or "retrograde analysis" puzzle. Raymond Smullyan wrote two delightful books of some very clever retro puzzles; check them out if you enjoy this sort of thing. – Eric Lippert Oct 1 '18 at 20:19

The Puzzle states: "The puzzle is a legal position from the starting position.". Black has still all pieces while white is missing 7 pieces. To get the black pawns "behind" the white pawns at least 8 pieces would need to be taken by the pawns (probably even more in the given position). With only 7 pieces missing this position is impossible.

This means that the orientation of the board is wrong once again. After rotating the board by 180 degrees, moving one of the pawns left or right from the king would be a valid non-mating move.

The puzzle title seems to be a hint as well.

• This was the intended answer. – Excited Raichu Oct 1 '18 at 16:47
• In the rotated-board scenario, given the positions of the white pawns, how would the black rooks have gotten behind? – tmpearce Oct 1 '18 at 16:50
• @Sleafar In a 180 degree rotated board scenario, no white pawns have moved 2 or more squares. – Keeta Oct 1 '18 at 17:10
• @tmpearce You are right. That makes my solution impossible as well. – Sleafar Oct 1 '18 at 17:13
• @ExcitedRaichu It seems your puzzle is unsolvable. See previous comments. – Sleafar Oct 1 '18 at 17:17

Well, given lateral thinking, some standard chess answers would be

resigning and/or offering a draw, both of which don't move the pieces.

• (+1) Not what I was thinking, but hey, it works! – Excited Raichu Oct 1 '18 at 16:23
• @Abigail really? I didn't know that. Thanks for the info! :D – Feeds Oct 3 '18 at 21:19

So with the board in its current rotation;

You can move either of the pawns abreast the King and not end up in checkmate in a single move on black's play.

We aren't told that the board is oriented correctly. Turn the board 180º then advance the pawn currently to the left of the king.

The given position is LEGAL with the board flipped and the edit.

1. d3 e5 2. Kd2 b6 3. Ke1 Ba6 4. Kd2 Bc4 5. Ke1 Be6 6. Kd2 Bf5 7. Ke1 Qh4 8. Kd2 Qxh2 9. Ke1 Qh6 10. Nc3 Be7 11. Nd5 Bh4 12. Bd2 Bg3 13. Bc3 Bh4 14. Qd2 Bg3 15. Qe3 Bh4 16. Qe4 Bg3 17. Qb4 Bh2 18. Kd1 Bxg1 19. Ke1 Qxh1 20. f3 Bf2+ 21. Kd2 Be1+ 22. Ke3 Bd2+ 23. Kf2 Bc1 24. b3 Bb2 25. Ke3 Qxf1 26. Kd2 Qxa1 27. Ke3 h5 28. Kd2 Rh6 29. Ke3 Rg6 30. Kd2 Rg3 31. Ke3 Rh3 32. Kd2 Rh1 33. Ke3 Rc1 34. Kd2 Nf6 35. Ke3 Ng4+ 36. Kd2 Nf2 37. Ke3 Nh3 38. Kd2 Ng1 39. Qa4 Kf8 40. Qb4+ Kg8 41. Ke3 Kh7 42. Kd2 Kg6 43. Ke3 Kg5 44. Kd2 g6 45. Qa3 Kh4 46. Ke3 Kg3 47. Kd2 Kh2 48. Ke3 Nh3 49. Kd2 Kg1 50. Ke3 Kf1 51. Qb4 Nc6 52. Qa3 Re8 53. Nb4 Re6 54. Nd5 Rd6 55. Nb4 Rd4 56. Nd5 Rh4 57. Nb4 Ng1 58. Nd5 Rh2 59. Qb4 g5 60. Bd4 Nd8 61. Qa4 Ne6 62. Bc3 Nf8 63. Qb4 Ne6 64. Ne7 a5 65. Qa4 b5 66. Qh4 b4 67. Qf4 bxc3 68. Qb4 axb4 69. Nd5 Ke1 70. Ne7 Kd1 71. Nd5 h4 72. Ne7 c6 73. Nd5 Ke1 74. Nc7 Bg4 75. Ke4 Bh5 76. Kf5 Bg6+ 77. Kf6 Be4 78. Na8 Bf5 79. Nc7 Ng7 80. Ke7 Ne6 81. Ke8 Ng7+ 82. Kf8 Ne6+ 83. Ke7 Bh7 84. Kf6 Bg8 85. Kf5 Nd8 86. Ke4 Ne6 87. Kf5 Bh7+ 88. Kg4 Bg8 89. Kf5 Nd8 90. Ke4 Bh7+ 91. Ke3 Bf5 92. Na8 Bh7 93. Nc7 Bg6 94. Na8 Bf5 95. Nc7 Ne6 96. Na8 g4 97. Nc7 g3 98. Nd5 cxd5

This is probably not the optimal way to do this, but it is possible.