A pleasing combination of ideas from the late Israeli Grandmaster of
Composition.
1.Ba2 sets up a diagonal battery and threatens 2.Bg5+ Kxe5 3.Qf4+ Ke6 4.c5. Black can defend by blocking c5, and the Grimshaw interferences between rook and bishop remove potential guards on f2 and g5, leading to two well-matched variations involving bishop switchbacks.
1...Rc5 2.Bxg3+ Kxe3 3.Bf4+ Ke4 4.Sf2;
1...Bc5 2.Bxh6+ Kxe5 3.Bf4+ Ke4 4.Sg5;
(also 1...Qf5 2.Sf2+ gxf2 3.Qg2).
Peter Niehoff: The mating squares f2 and g5 are guarded by black pawns, which can be removed by the white bishop, but the black king also removes pawns, unveiling new guards. The surprise key leads to Grimshaw interferences which neutralise these new defences.
Dafydd Johnston: The potential Grimshaw on c5 is not difficult to spot, and the challenge for the solver is to find the key that will persuade Black to occupy that square and set the mechanism in motion.