DIAGRAM 30.

It is White's move. If Black's Queen did not protect the Pawn f7
White would be able to give a mate in five moves, thus: (I)
Rxf7+, K-g8; (2) Rxg7+, K-h8 (not K-f8 on account of Rc7-f7
mate); (3) Rxh7+, K-g8; (4) R-g7+ and Kt-g6 mate.

Therefore, White will try to interrupt the diagonal in which the
Queen defends the threat, and he can do so by (1) Kt-d5. Black
being unable to keep f7 protected, must defend g7 or h7, or he
will be mated. In the game in question Black played Q-a1+ ; (2)
K-g2, P-a3. After (3) Rxf7+, K-g8 it would not be good for White
to take g7, giving up the two Rooks for the Queen, as he would
then have no more attack while Black still has the dangerous Pawn
in the a-line. If possible he will rather interrupt again the
diagonal of Black's Queen. This suggests the move (4) Kt-f6+.
After Pxf6 White's Rooks are at last free to act unmolested in
the seventh rank, and they do it with deadly effect. White forces
the mate through (5) R-g7+, K-h8; (6) Rxh7+, K-g8; (7) Rh7-g7+,
K-h8; (8) B-f5! Now R-g4 is threatened followed by R-h7 mate, and
Black has no defense.

In the opening and in the middle game the main threat of a Rook
is the "pinning" of a hostile piece. What is meant by this is
illustrated in Diagram 31. Supposing Black, to save his Knight f6
which White has just attacked by P-e5, plays Kt-g4 and after (2)
P-h3 takes the Pawn e5 with the Knight g4, then White wins a
piece by (3) Ktxe5, Ktxe5; (4) R-e1. This move "pins" Black's
Knight to his place as the King would be exposed to White's Rook