a)

1.Sd4? ~ 2.Bf6 Ke4 3.Kg3

3...Kd5/Ke34.Qc6#/Qe2#

2...Kc5 3.Qb5+ Kd6 4.Qc6#

1...Kc5 2.Be3 Kb4 3.Qb5+

3...Ka3/Kc3 4.Qb3#

2...Kd5 3.Qc6+ Ke5 4.Qe6#

but: 1...Kxd4!

1.Bc1?

1...Ke4 2.Qc6+ Kd3 3.Kg2 Ke2 4.Qc2#

2...Kf5 3.Kg2 Kg4 4.Qg6#

but: 1...Kc5!

1.Be3?, Ke4!;1.Kg2?/Kg3?, Kc5!

1.Bf4?

1...Kc5 2.Sd2 Kb4 3.Qc4+

3...Ka3/Ka5 4.Qb3#/Bc7#

but: 1...Ke4!

1.Bf6? ~ 2.Sd4 Ke4 3.Kg3

3...Kd5/Ke34.Qc6#/Qe2#

2...Kc5 3.Qb5+ Kd6 4.Qc6#

but: 1...Kc5!

1.Sd2!

1...Kd4 2.Qc4+ Ke5 3.Be7 Kf5 4.Qe4# MM

1...Kc5 2.Bf4 Kb4 3.Qc4+

3...Ka3/Ka5 4.Qb3#/Bc7#

1...Ke5 2.Qc6 Kd4 3.Bf4 Kd3 4.Qc4#

2...Kf5 3.Be7 ~ 4.Qe4#

3...Kg4 4.Qf3#

b) 

1.Bc1?

1...Ke4 2.Qc6+ Kd3 3.Kg2 Ke2 4.Qc2#

2...Kf5 3.Kg2 Kg4 4.Qg6#

but: 1...Kc5!

1.Qe2?, Kc6!;1.Be7?/Bb4?/Kg3!, Ke4!;1.Qg6?, Kc4!

1.Qa4? ~ 2.Sg5 Ke5 3.Be7 ~ 4.Qe4#

but: 1...Ke6!

1.Sg5!

1...Kd4 2.Bb4 Ke3 3.Qe6+

3...Kf2/Kf4 4.Qe1#/Bd2#

3...Kd4/Kd3 4.Qe4#

2...Ke5 3.Qe6+ Kd4/Kf4 4.Qe4#/Bd2#

2...Kd5 3.Qe6+ Kd4 4.Qe4#

1...Ke5 2.Qe6+ Kd4 3.Bb4 ~ 4.Qe4#