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Blockage Detection in King and Pawn Endings

The conventional search methods using static evaluation at leaf nodes are liable to missing the fact that no win goal exists in certain positions. Blockage positions, in which neither side can penetrate into the opponent’s camp, are a prominent example of such positions. Deep search cannot detect the existence of a blockage, since its judgment is based solely on static evaluation, without taking the goals into consideration. In this paper we introduce a blockage detection method, which manages to detect a large set of blockage positions in pawn endgames, with practically no additional overhead. By examining different aspects of the pawn structure, it checks whether the pawns form a blockage which prevents the king from penetrating into the opponent’s camp. It then checks several criteria to find out whether the blockage is permanent.