Corresponding Squares: Triangulation with an Advanced Passed Pawn
White to play and win, after Fahrni - Alapin
PlayYour c6 pawn is one square from the seventh rank, and the black king blockades on c8. The win is a map of corresponding squares, and it comes down to one simple fact: you have a spare square, and he does not.
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Corresponding Squares Behind the Passed Pawn
White to play and win · Win against perfect defense
Waking the engine…
The theory
Watch the method: press play to see the winning idea run, or step through it move by move.
Two reciprocal zugzwangs jump out first: d6 against d8, and c5 against c7. In each pair, whoever is to move loses the argument. Those two pairs create a third one: d6 and c5 both touch d5, while d8 and c7 both touch c8, so d5 corresponds to c8. That is exactly where the kings stand, but with you to move, which is the wrong way round.
This is Fahrni against Alapin, 1912, the standard exercise for building a corresponding-squares map from scratch.
Start with the obvious pairs. Kings on d6 and d8 is reciprocal zugzwang. So is c5 against c7. In both, whoever is to move has to give way.
Extend the map. d6 and c5 both touch d5; d8 and c7 both touch c8. So d5 corresponds to c8. That is the position in front of you, with you to move, which is the wrong way round.
Count the spare squares. Adjoining d5 and c5 you have two more: c4 and d4. Adjoining c7 and c8 Black has only d8, because the c6 pawn covers b7 and d7. That one extra square is the whole win: Kc4 Kd8, Kd4 Kc8, Kd5 and the map is back with Black on move.
In this drill the defender knows the map too. Kd6, Kc8, c7 and the pawn queens.
Keep going
The Stalemate That Saves
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Corresponding Squares: Dedrle's Draw
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The Wing Pawn Is Bait
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All 68 king & pawn positionsFollow the full curriculum (free)