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King + Two Bishops vs King

King and two bishops against a lone king is a win, and the two bishops work on opposite colours to drive the king into a corner. One bishop gives check, and the other bishop takes the king's last escape square.

The finished shape

This is the finished shape. King and two bishops against a lone king is a win, and the two bishops work on opposite colours to drive the king into a corner.

FEN: 7k/p5B1/6K1/3B4/8/8/8/8 b - - 1 1

a b c d e f g h
8 . . . . . . . k 8
7 p . . . . . B . 7
6 . . . . . . K . 6
5 . . . B . . . . 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. One bishop gives check, and the other bishop takes the king's last escape square.

FEN: 7k/p7/6KB/3B4/8/8/8/8 w - - 0 1

a b c d e f g h
8 . . . . . . . k 8
7 p . . . . . . . 7
6 . . . . . . K B 6
5 . . . B . . . . 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/p7/6KB/3B4/8/8/8/8 b - - 0 1

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

Key points

  • One bishop gives check, and the other bishop takes the king's last escape square.
  • The worked example ends with Bg7.
  • 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.