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Explanation
Two bishops that travel on opposite colors, together with their king, can checkmate a lone king. One bishop controls light squares and the other controls dark squares. Together they form a diagonal wall the enemy king cannot cross, while the attacking king takes away the remaining space.
How the net closes
The bishops are usually kept coordinated on neighboring diagonals. The attacking king advances behind that barrier and gradually reduces the available area. The final mate occurs on an edge, often in a corner, where one bishop checks and the other bishop and king cover the exits.
Unlike , any corner can work because the bishops cover both square colors. Two bishops that travel only on the same color, which can occur if two pawns reach the far edge and are turned into bishops, cannot force this mate against a lone king.
Common confusions
Two bishops and bishop plus knight
With two opposite-colored bishops, mate can be delivered in any corner. With bishop and knight, the king must be driven to a corner matching the bishop's square color.
View termTwo bishops on the same color
Two bishops that travel on the same square color cannot cover both light and dark squares and cannot force mate against a lone king. The basic mating pair needs one light-squared bishop and one dark-squared bishop.
Sources
- 1.Checkmate With Two Bishops, Chess.com
- 2.Piece Checkmates II, Lichess