Lesson
White to move. Main line: 1. Bxg7#
Bxg7# checks h8 from the adjacent diagonal and removes one of the king’s pawn shields. The bishop is protected by the king on f6, so Kxg7 is not a legal response.
The queen on e6 controls g8, and Black’s own pawn remains on h7. Since a bishop’s contact check cannot be interposed against, the king has no capture, block or flight available.
Bishops can mate when other pieces solve their color-complex limitation. Here the queen controls the light square g8 while the dark-squared bishop gives check; coordinated coverage matters more than the nominal value of the mating piece.