Solution: 1...Kb3 has a set continuation 2.Qe2 followed
by 3.Sb6. The queen would like access to d7 to cope with 1...Kb5,
and this requires the king to clear the diagonal. If White tries
1.Kg6? a random move of the bishop can be met with 2.Sd6,
confining the king in preparation for a queen mate, but Black
has the subtle defence 1...Bxf4, after which 2.Sd6 delivers
stalemate. White anticipates this defence by playing
1.Ke4! and now everything works. 1...Kb3 2.Qe2 any
3.Sb6, 1...Kb5 2.Qxd7+ Ka6 3.Qb7, or 2...Kc5
3.Qc6, and 1...B any 2.Sd6 Bxd6 3.Qxd7.