White must he careful not to stalemate the Black King. For instance, if Black were to play here 15. ... K to R sq., White could not play 16. B to K B 5; but must play 16. B to K 3, K to R 2; 17. B to B 5: ch., K to R sq.; 18. B to Q 4 mate.

16.B to K 3: ch.16.K to R 2
17.B to B 5: ch.17.K to R sq.
18.B to Q 4, checkmate.
KING, BISHOP, AND KNIGHT AGAINST KING.

To checkmate with Bishop and Knight is a very difficult process. Checkmate can only be forced if the Black King is driven to one of the Rook squares of the same colour as the Bishop. In the position shown in Fig. 20 the Black King must be driven either to Q R sq., or K R 8. Frequently the Bishop and Knight are separated from the White King; in that case the Black King cannot be prevented from moving to a Rook square of the opposite colour to the Bishop. Then the forces must be brought together to act in concert with the White King; when, by combined action, the Black King can be forced on to a corner square of the same colour as White's Bishop, and checkmated as shown in the appended solution. Mate can be forced in the most

unfavourable position (see Fig. 20) in about thirty or thirty-one moves.

WHITE.BLACK.
1.Kt to Kt 3: ch.1.K to B 3

If 1. ... K to B 5; then 2. B to Q sq., K to B 6; 3. K to Kt 5, K to Q 6; 4. K to B 5, K to K 5; 5. B to B 2: ch., K to K 4; 6. Kt to Q 4, K to B 3; 7. K to Q 6, K to B 2; 8. Kt to B 3, K to B 3; 9. Kt to K 5, K to Kt 2; 10. K to K 6, and the King is gradually forced on to the last row.

2.K to Kt 42.K to Q 4
3.B to B 3: ch.3.K to Q 3
4.Kt to Q 44.K to K 4
5.K to B 55.K to B 3
6.K to Q 56.K to B 2
7.Kt to B 57.K to B 3
8.Kt to Q 68.K to Kt 3
9.K to K 59.K to Kt 2
10.B to K 410.K to Kt sq.
11.K to B 611.K to R sq.