Retractor

In retractor chess problems, your task is to take back one or more moves to reach a position where you can achieve a specific goal, like delivering checkmate. The challenge involves figuring out which moves to retract and then finding the correct moves to achieve the goal from the adjusted position.

Common scenarios in retractor problems include:

Retracting White's last move: Undo White's most recent move and then find a way to checkmate in one move.

Retracting moves from both sides: Take back the last move made by White and the last move made by Black, then play forward one move by Black and one move by White, where White delivers checkmate.

When retracting a capture, you typically need to specify the piece that was captured as well. For example, if you're undoing a move where the king on b3 captured a rook on c4, you would write "KxRc4" instead of just "Kxc4". In Advent of Chess, however, we typically only require the moves needed to play forward after the retraction for the solution (but the required format will be specified for each problem).