in der Retroanalyse
12 - J. G. Mauldon
British Chess Magazine, 1966
[15+10. (RV) Matt in 3 Zügen]
Suppose black can castle both king- and queenside. Then his last move
was either b7-b5, d7-d5 or f7-f5.
Suppose now black can't castle queenside. Then #3 with 1. Bd6!, and
(again) black has no proper defense against 2. Rh8 or 2. Ra8.
And the last case: Black can't castle kingside. Then #3 with 1. Bf6!
Solution by Philippe Schnoebelen