Black begins: 1.Ba5 Be4 2.Rf5 Bc6#
White begins: 1.Rh5 Re4 2.Bc4 Re6#
Reason for choice: I have always been fascinated by problems
in which the play of each side imitates the other, either
formally or strategically, or both. The natural home for
such work is the duplex helpmate, in which not only does
Black help White to mate, but White proceeds to help Black
to do the same: both sides fulfil the stipulation. This
problem, by a very talented Indian composer, was an
inspiration to me when I was first attempting this form of
composition. The strategic correspondence of the two parts
is perfect. The first move is a self-block, the second an
interference-unpin on e4 (at the same time opening an
essential line), the third is a reciprocal unpin by the
unpinned piece, allowing mate by double check on the fourth. Beautiful. And note how all 6 line-pieces participate in both parts. Who could ask for more?