Mate in 4

1.Bc6+ Kxd3 2.Bb5+ Ke4 3.Qd8 threat 4.Qd3 (which becomes a model after 3...Bxf2); 3...Kf3 4.Qa8 (model mate); 3...Kf5 4.Bd3 (model mate). If 2...Kd4 3.Qb4+ Kd5 4.Qc4.
The original setting contained a superfluous black pawn at a7.
The problem gives the impression of being a built-up two-mover, a type which was common in the 19th century. The main idea appears to be the three model mates, which could be shown in a much lighter two-mover with an acceptable key. The composers have introduced difficulty and a little surprise by adding the sacrificial introduction, which, I think, makes for a more interesting problem.