1.Bxc5! threat: 2.Bf2 threat: 3.Sg3#

2...f4 3.Sg3+ fxg3 4.Bc4#

1...Ke1 2.Bb4+ Kf1 3.Be6 f4 4.Bh3#

2...Kd1 3.Bb3#

1...f4 2.Be6 Ke1 3.Bb4+ Kd1 4.Bb3#

    3...Kf1 4.Bh3#