()English (United Kingdom)
francesco.simoni(25.01.2015) , .

509. Francesco Simoni (Italy)
H#2 b) Sa2-b1 (8+15)
a) 1.Sc1 Qxb2+ (Rxb2+?) 2.Se2 Sdf4# [1Rxb2+? 2.Se2 Se1?]
b) 1.Re6 Rxb2+ (Qxb2+?) 2.Re2 Se1# [1Qxb2+? 2.Re2 Sdf4?]

Black moves a piece twice, to indirectly unpin the mating one, with reciprocal dual avoidance for black line opening. The unpinning piece however, would avoid the mate for direct guard, so white has to check, to force the direct self-pin of the black piece and to perform so a pin mate.
In W1 there is reciprocal dual avoidance for loss of guard ie. White could check with any of the two units, but just what will be replaced by the mating piece as flight controller can only be chosen. (Author)

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