Eat or run — the square backwards

White wins White to move · Pawn endgames · Difficulty about Elo 1100

The plan

The white king could eat the enemy pawn — but MAY he? The rule of the square answers that in a second, if you apply it the right way round: picture a square from your own pawn to the queening rank and ask whether the enemy king can enter it before the pawn gets through — and calculate it BACKWARDS, that is before the capturing move, not after. Here the answer is yes, and that is why it is not the king that wins, but the pawn: measured, exactly ONE of the six moves holds the win, namely the pawn step, while all five king moves, including the capture, are now only a draw. How razor-thin the border runs is shown by shifting the black king by a single file: one file further out, even the greedy capture wins; one file further in, the position is only a draw even with the best move. There is one exception to remember, or you calculate the square too large — the pawn on its home rank may move two squares. This too is measured: the same pawn on the second rank is only caught by kings on five files, one rank further forward by six.

Rule of thumb: calculate the square backwards first, then eat — and with a pawn on its home rank, count from the third rank.

Why this level: The rule of the square in your head; only one of six moves wins

The solution, move by move

1. 1. c6 The only winning move of six! 1.Kg5? Kf7! is the costly mistake: White does eat the h-pawn, but the black king reaches the square of the c-pawn — a draw (sideline).
   Sideline 1. Kg5 The greed: the king goes to eat without calculating backwards. 1… Kf7 2. Kxh5 Ke6 While White is chewing on the edge, Black marches: e6, d6 — straight into the square of the c-pawn. 3. c6 Kd6 4. c7 Kxc7 The pawn falls: a draw. One look at the square BEFORE eating would have saved the whole point.
2. 1… Kf8 Black storms back — but the square of the c6-pawn only reaches to the e-file: f8 stands one step short. This one file is the whole difference. [%csl Ge6,Ge7,Ge8,Rf8]
   Sideline 1… h4 The counter-race: the h-pawn storms off — 2. c7 h3 3. c8=Q — but the queen arrives one move sooner and already covers h3 from c8. The pawn falls, White wins.
3. 2. c7
4. 2… Ke7
5. 3. c8=Q The queen has arrived and aims straight down the diagonal from c8 to h3 — that is why the h-pawn's counter-race (sideline) was hopeless too.

More in Pawn endgames

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• One pawn holds two — the saving trade Draw
• The stalemate trap — pawn on the sixth White wins
• Corresponding squares (Lasker-Reichhelm 1901) White wins
• Connected passed pawns — advancing under cover White wins
• Wing majority 3 against 2 — the candidate first White wins