15+10. Matt in einem Zug!
Suppose black moved last. Then his last move must've been e7-e5. White's
last move was either Bh2xg3 or Kf4-f5. If it was the latter, black's
move before that must've been g6-g5. But that implies that the h-pawn
promoted on g8 to a knight, not on h8. So in both cases, white captured
a piece on the g-line. If black's last move was e7-e5, this also means
that Bd4 is promoted. The only pawns that could promote on a black square
without capturing are the a- and the c-pawn. If the a-pawn promoted,
the white a-pawn must have captured 3 times on its way to b8 or d8 (where
it promoted to a bishop). Together with the 2 captures on the c- and
d-file, the capture on the g-file, and the bishop on f8, this is 7 captures.
So black's a-pawn didn't promote. If the c-pawn promoted, white must've
captured b2xc3 and cxd. Together with a7xb8, Bf8 and the promotion on
g8 this equals 5 captures. But none of these captures happened on the
a-file. So the c-pawn couldn't have promoted either. So black didn't
move last. So #1 with 1. ... Nh6!#
Solution by Philippe Schnoebelen
