1) BD6+ CD
This is one of the two examples of Forced Positioning in this endgame combination, here the B "Sac" sets up a future pin of the D7 pawn. If the Q captures then of course the Knight has a nice family fork.
2) KC3 KA2
White threatens a "horizontal king and rook edge mate" and black moves his King to prevent this.
3) RB2+ KA3
If 3)... KA8 then 4)NC2 is a Rook Knight Mate mate
4) RB7! KA2
5)KC2 KA3
6)RA7+ KB4
The Black King was forced into a square where the White Knight can now fork it and its Queen. This is the second example of Forced Positioning in this combination.
7) NC6+
The Queen is lost if the King moves due to the family fork. or if the pawn captures the knight due to the Pin of the Pawn by the Rook which was set up by the opening BSac.
