This week’s problem is by one of the greats, and an excellent demonstration of
mate transference. Note the set play, but don’t be fooled by it!
There is set play, in that Black has four pawn moves, which would allow mates by
interfering with the actions of the bQ: 1...c6 2.Bb6#; 1...e6 2.Rxc7#; and 1...g6
2.Qxe7#; 1...g5 2.Qc1#. There is also 1...d3 2.Qc3#, which is unthematic.
One might be tempted therefore to think that the position is a block problem, but
it is not. The key 1.Sd6 threatens 2.Sb7#. The four possible captures of the knight
see the same four mates reappearing from the set play phase, but after different
defences: 1...cxd6 2.Bb6# 1...exd6 2.Rxc7#; 1...Kxd6 2.Qxe7#; 1...Qxd6 2.Qc1#, a
fine example of mate transference, where the defences change between different
phases of play, but the mates do not.