Retractor

retractor chess problem

An oldie but a goodie:

From this position, White retracts his last move, then Black retracts his and replaces it with a move that permits White to mate him immediately.

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The white king had just moved from g6, capturing a black rook on h5. That rook had just captured a white queen. So if we back up two steps, the position is this: Now if Black castles, White can mate him on the move: Julio Sunyer, Chess Amateur, 1923.