A clear-cut problem in which the starting point should be examination
of the two black captures.
The black captures in the diagram have mates set: 1..Sxd5 2.Se2 and 1...Sxg5 2.Qf2. King tries to support a threat of 2.Be3 mate fail because the set mate is obstructed: 1.Ke2? Sxd5! and 1.Kf2? Sxg5! 1.a3 threatens 2.Rxc4+ Kxc4 3.Qb4, leading to two variations where the defence allows a new mate which replaces a set mate 1...a5 2.Ke2 threat 3.Be3; 2...Sxd5 3.Sb5; 2...Sxg5 3.Qf2 and 1...Bc5 2.Kf2 threat 3.Be3; 2...Sxg5 3.Qf6; 2...Sxd5 3.Se2.