14+12. Matt in einem Zug
a)
Black's last move can't have been c6-c5, because
this would imply a retroplay like -1. ... c6-c5 -2. Qc7-b6 b6xNa5
-3. Be4-f3 Kg2-g1 -4. Bd3-e4 Kg1-g2 and now the only way to
open the northwest cage is to uncapture a darksquared black bishop on
b4, bring it to f8, and retract e7-e6; but then both black rooks would
be caught in the cage. Thus the last move was c7-c5 with a retroplay
like -1. ... c7-c5 -2. Qc6-b6 b6xNa5 -3. Kd1-e1 Kf1-g1,
also showing that white can't castle. The only solution is 1.
b5xc6 ep#
b)
Now the last move could be c6-c5, with retroplay
like -1. .. c6-c5 -2. Qc7-b6 b6xNa5 -3. Be4-f3 Kg2-g1 -4. Bd3-e4
Kg1-g2 and the cage is opened by retracting the white rook
to h8, the white queen to d8, and the black pawn on c6 to c7, and then
uncapturing c6xb7. So white may not capture en-passant. But this retroplay
also shows it's possible to preserve white's queenside castling rights.
So #1 with 1. OOO#
Solution by H. Juel
