Solution to chess problem number 4
The clue to the theme of this problem resides in the line up of three rooks on the 5th rank. In the diagram both black rook are half-pinned. Thus if one moves then the other becomes fully pinned and thus unable to move. White exploits this line with the key move
1. Bf2 threat 2. Bg3 mate.
This forces one of the rooks to defend this threat and in doing so the other rook becomes fully pinned and so cannot prevent an alterative mate. In the course of these rook moves black also interferes twice with the line of the black bishops which would also stop the intended white mates.
1...Rc4 2. Nd3 mate, 1...Rd4 2. Nc6 mate,
1...Rc3 2. Bd4 mate, 1...Rd3 2. Nc6 mate.
White has a number of other attempts (or tries) to exploit the half-pin set up but each fails as follows:
1.Kh1 Rc1!, 1. Be3 g5!, 1. Bxc5 Bb5!, 1. Kh3 R checks.