Bishop and Pawn vs Bishop: The Short Diagonal

In same-color bishop endings the defender holds by controlling the square in front of the pawn, switching between the two diagonals that cross it. That is the whole defense, and it has one condition.

The short diagonal. Both diagonals must be long enough to live on. Here b7 is crossed by the long a8 to h1 line and by a6 to c8, which is only three squares long: a6, b7, c8. Once White's bishop sits on b7 the defender is left with a6 and c8, and a diagonal that short falls when the attacking king and bishop cover all of it.

The method. Occupy the long diagonal's key square with your own bishop, protected by the king, so the defender is pushed onto the short one. Then attack him there. He runs out of moves.

Zugzwang does the work. With the bishop tied to c8 and the king tied to a6, Black has nothing to move. Bishop endings are decided by zugzwang far more often than by tactics.

The rule of four. Count the squares on each diagonal that crosses the pawn's stopping square. If both are four squares or longer, the defender holds. If one is shorter than four and your king and bishop together cover the whole of it, you win. The bishop can only take one square from its rival, so the king must cover the rest. And this applies at the pawn's last stop. Further back, breaking one blockade only brings you to the next.

In this drill the defending king is perfectly placed and it does not save him. Do not push the pawn, maneuver the bishop.