14+11. (RV) Matt in 3 Zügen
If black still can do both castlings, his last move must've been d7-d5
or f7-f5, since a pawn capture on d5 or f5 would take too many captures.
- Black's last move was d7-d5: #3 with 1. cd6! Ra5 2. Ra5 ~ 3. Ra8#.
- Black's last move was f7-f5: #3 with 1. gf6! and black has no defense
against 2. Ng7 Kd8/f8 3. Qh8#.
Now suppose black can't castle queenside. Then #3 with 1. Ng6!
The last case is: Black can't castle kingside. Then #3 with 1. Nc6!.
Solution by Philippe Schnoebelen
