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Vladimir Nabokov composed chess problems. Here’s a clever one from 1932: “White retracts its last move and mates in one.”
This is an instance of retrograde analysis: Of the many legal moves that White might just have made, only one can be revised to yield an immediate mate. Can you find it?
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White’s last move must have been an underpromotion, with a pawn on d7 capturing a knight on c8. If we retract that move we get the position above, and if the pawn instead now captures the rook on e8 and promotes to a knight, it gives mate. This is the only legal possibility that meets the requirements of the problem.
Nabokov writes, “There is some mild magic in the retrospective transformation of White R into Black Kt, and Black R into White Kt, with the symmetry of the pieces (and White’s defense of c7) retained.”
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