The square of the pawn
A quick visual trick to decide if the enemy king can catch a passed pawn.
When a passed pawn races toward promotion and the enemy king tries to catch it, you do not need to calculate move by move. Just draw a mental square.
Picture a square from the pawn's current square to the promotion square (the two far corners). If the enemy king can step into that square on its next move, it catches the pawn and draws. If it cannot step in, the pawn promotes no matter what the king does.
This single trick saves enormous calculation time in pawn races. It works because the king and a pawn advance at the same speed - one square per move - so the geometry is exact.
Examples
Black king is outside the square - pawn promotes
The pawn is on g4, promoting on g8. The 'square' has corners g4, g8, c8, c4. The Black king on a4 is outside this box - it cannot reach c4, c5, c6, c7, c8, d8, e8, f8, or g8 in time. White plays g5 and the pawn queens without being caught. No calculation needed.
King is inside the square - pawn will be caught
The pawn is on d4 promoting on d8. The square has corners d4, d8, h8, h4. The Black king on c1 steps to c2, then c3, entering the square before the pawn gets far. Even though the king looks distant, it intercepts the pawn before d8. This is a draw - the king is inside the square.
Key terms
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