13+11. Matt in einem Zug!
Bl. caps are a7xb6, bxc and wPf on its f-file. For balance, the wPg2
did promote on h8 after g6xh7. Other wh. caps are d2xc3, a2xb3xc4 and
bBf8 at home. This accounts for all captures.
The position unlocks by (1) unpromoting a wR on h8,
(2) resurrecting bl. QB through g6xBh7, (3)
reconducting this bB to c8, (4) retracting b7-b6 and
later b6xc5, (5) thus freeing wNa4 and then wBb1.
Unpromoting a wR requires that it uses the d1-a1-a3-b3-b5-a5-a7-b7-b8-h8
corridor. But there is a bR trapped in the corridor right now and the
only way to eventually unpromote a wRh8 is to assume that wKe1 did move,
so that the bRa1 can be freed. In conclusion, Wh. cannot castle.
Solution: 1. Tf1# and not 1. 0-0 ??
Solution by Philippe Schnoebelen