P-9A (The Rule of the Square)

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A distant black king has some prospects against the pawn only if the white king is unable to support it by controlling the critical squares on its way to the eighth rank (cf. diag. 9) . In this case the vital question “can the black king catch and capture the white pawn on its way to promotion”, may be answered quickly and without any calculation by using the “rule of the square”. The imagined square is formed in such a way that one side is made up of the pawn and its promotion square, the third corner is found by drawing a diagonal from the pawn to the eighth rank, the fourth corner is at the intersection of the pawn’s rank and the third corner. The exception to the rule is the pawn in the initial position since it may advance two squares on move one: its square is formed with the corner on the third rank. The rule states: “if the black king is within the square or may be able to get into it, the game is drawn” as the black king will be able to catch the pawn. If that is not the case, the pawn is quicker. This peculiarity is due to the specific geometry of the chess-board whereby the diagonal of the square equals its sides. From the a1-square, the king takes the equal number of moves to reach h8 or a8! Therefore, we can easily evaluate the position in diagram 9.



The rule of the square

c4 pawn square. If black king can enter the square, he will stop the pawn


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GM Vlatko Kovacevic

Vlado Kovacevic is a chess grandmaster and an endgame expert. He very successfully competed on the national team. From 2000 – 2004, he acted as selector of the Croatian Men’s national team. He is also a well-known chess author.