BDSPeter Fayers & BDS
The Problemist Supplement, 1997
H#3
Circé Exchange
1.Bxd2[+wSa5] Sxc4[+bSa5] 2.Sxb7[+wBa5] Sxd2[+bBc4] 3.Ba2 Bc3#
Before a mate can be constructed, both bishops have to change their square-colours.
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