Solution to Chess Problem 3
The idea of this problem is to illustrate the concept of changed themes. If if were black to move in the diagrammed position the obvious captures on f3 would lead to some self-block mates. In this case the escape of the black king to f3 is blocked by his own piece:
1...Nxf3 2. Qg4 mate or 1... Rxf3 2. Qe5 mate.
The key move 1. Qh1 threatens 2 Re3 mate and forces black to capture on f3 and thus self-pin the capturing piece. Thus the theme of self-blocks have been converted to one of self-pins.
1...Nxf3 2. Rd4 mate or 1..Rxf3 2. Nc3 mate.
Note that the key move gives a flight square for the black king but if this is taken then a rook shut off (in which the action of the black rook on a3 is prevented) using the queen and rook battery allows mate:
1...Kd5 2. Rc3 mate.