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Antichess, also called losing chess, loser's chess, zero chess, and suicide chess, is a chess variant in which the objective is to lose all of your pieces. The most widely played variation, as described in the book Popular Chess Variants by D.B. Pritchard, is described below.
The rules of the game are the same as those of chess except for the following additional rules:
A player wins the game either by losing all his pieces or by forcing the opponent to stalemate him so that he has fewer pieces than his opponent. The game might be drawn, apart from move repetition or mutual accord or the 50-move rule, when it is impossible to get a win; for example, if a dark-squared bishop and a light-squared bishop are the only pieces remaining. In another little-played version, forcing your opponent to checkmate your king is another option to win.
Because of the forced capture rule, antichess games often have a long sequence of forced captures by one player. This means that a minor mistake can ruin the whole game. Losing openings include 1.b4, 1.d3, 1.d4, 1.e4, 1.f4, 1.h3, 1.h4, 1.Nf3 and 1.Nc3 (algebraic chess notation). Some of these openings took months of computer time to solve, but the wins against 1.d3, 1.d4, and 1.e4 consist of a single series of forced captures, and can be played from memory by most experienced players.