I found mate in 4 with 1.Qb3, instead of 1.Qb2

Oh!

I saw this mate pattern quickly, but it took one hour to find a way how to make the black king move onto c6.

V-1

1.Qb2 Kd7
2.Qe5 Kc6
3.Qd5#

V-2

1.Qb2 Kd7
2.Qe5 Kc8
3.Qc7#