BDS
Problemskak, 2021
#2
KöKo
ROOK-HOPPER b5
BISHOP_HOPPER a3, a4
1.Ba2! () 1...c3 2.Re4# 1...Bg5 2.Sf6# 1...Bf4 2.Se3# 1...Bb4 2.Bc5# 1...Bc3 2.Rd8#
The black pawn is not pinned after the key – if it moves the black king is not in check from the white bishop a2 because there in nothing adjacent to d5. After 1...c3, though, White can play 2.Re4, when there is something adjacent to d5 and so the black king is in check. 1...Bg5 and 1...Bf4 allow the white knight to mate by moving adjacent to the black bishop. In both cases black move has ruled out 2...c3. 1...Bb4 guards c5, allowing 2.Bc5#. 1...Bc3 allows 2.Rd8#. The bishop moving has ruled out 2...c3. Other black bishop moves, though also stopping 2...c3, defend against 2.Rd8 as the bishop can defend on the d-file.
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