Discussing the problem presented on pg 145, ‘Moriarty Problem M1’ from The Chess Mysteries of Sherlock Holmes by Raymond Smullyan; the official solution, an alternate solution, and a potential modification to the problem
The solution Smullyan presents is indeed elegant; if we take our starting board to be:
The white bishop moves to e8, discovering check from the white rook; the black bishop moves to h4 to block check and discover check from black rook; the white knight moves to e1 to block check and discover check from the white bishop, and the black Queen moves to g4 to block check. Therefore, Smullyan tells, us, the last move was the Black Queen from e4 to h4.
But there is a much much simpler solution. If the earlier state of the board were, for example:
Making the last move the rather innocuous Pawn to g7 to g6. In his solution on page 163, Smullyan challenges the reader to “Try any other last move, and you will find it impossible to play back three more moves.” I couldn’t find any problem with the above sequence. A very simple correction to the position that would render Smullyan’s (far more interesting) solution as exclusively viable could be:
Note that this requires an additional capture by a black pawn on g6 (either from f7 or h7) somewhere in the history of the game, but this does not appear to create any specific contradiction on the board. We should be mindful that:
- White has at least one promoted bishop on the board (which would have had to promote on a8, c8, e8, or g8)
- White has made at least two captures with pawns (not the d and g file)
But neither element seems to restrict the above position from being legally attained.