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BDS

The Problemist, 1978

#2
Circé Antipodean

1.Qc7!          (2.Sd6#)

1...Rxh2 [+wPd6] 2.Qc5#
1...Sxh2 [+wPd6] 2.Qc6#
1...e5           2.Qc4#
1...Bf4,Ba5      2.R(x)a5#
1...Bb4          2.a4#

In the first two variations, Black defends by taking a pawn that is then reborn on the threat square. However, both of these moves make the error of opening a line from a potential mating square to a potential rebirth square, so allowing the white queen to guard itself in mating. 1...e5 opens another rebirth line and allows another self-guarded mate by the queen. The variations are mopped up by a couple of unguards and a self-block, all courtesy of the black bishop. I was so happy with the airy construction (the bSe1 is the only plug), that I failed to notice how bad the key was, but the solvers told me all about it!