King + Bishop + Knight vs King

King, bishop, and knight against a lone king is a win, and the bishop and the knight cover different escape squares around the corner. The knight gives check, and the bishop and the king take the king's escape squares.

The finished shape

This is the finished shape. King, bishop, and knight against a lone king is a win, and the bishop and the knight cover different escape squares around the corner.

FEN: 7k/p4N1B/6K1/8/8/8/8/8 b - - 1 1

a b c d e f g h
8 . . . . . . . k 8
7 p . . . . N . B 7
6 . . . . . . K . 6
5 . . . . . . . . 5
4 . . . . . . . . 4
3 . . . . . . . . 3
2 . . . . . . . . 2
1 . . . . . . . . 1
  a b c d e f g h

The worked example

White plays the mating move here. The knight gives check, and the bishop and the king take the king's escape squares.

FEN: 7k/p6B/6K1/4N3/8/8/8/8 w - - 0 1

a b c d e f g h
8 . . . . . . . k 8
7 p . . . . . . B 7
6 . . . . . . K . 6
5 . . . . N . . . 5
4 . . . . . . . . 4
3 . . . . . . . . 3
2 . . . . . . . . 2
1 . . . . . . . . 1
  a b c d e f g h

How to prevent it

Black plays a6 first. The pawn move opens an escape square, so the mate no longer works.

FEN: 7k/p6B/6K1/4N3/8/8/8/8 b - - 0 1

a b c d e f g h
8 . . . . . . . k 8
7 p . . . . . . B 7
6 . . . . . . K . 6
5 . . . . N . . . 5
4 . . . . . . . . 4
3 . . . . . . . . 3
2 . . . . . . . . 2
1 . . . . . . . . 1
  a b c d e f g h

Key points

The knight gives check, and the bishop and the king take the king's escape squares.
The worked example ends with Nf7.
To prevent it, keep the king off the corner and keep an escape square open.
Black plays a6 first. The pawn move opens an escape square, so the mate no longer works.
Check every escape square before you play the mating move, because one open square breaks the mate.

Try it Yourself

Edit the code, then press Run.

Running is simulated · Rust Playground

Exercise

Find the checkmate in this position.

Nf7# Bg8 Kf7 Kh6