Perpetual check
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In the game of chess, perpetual check is a special case of draw by threefold repetition, in which one player forces the repetition by a series of checks.
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| Unzicker-Averbakh: perpetual check extricates Black from his difficulties. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Hamppe-Meitner: down massive amounts of material, Black forces a draw by perpetual check. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
In the diagram at left, from Unzicker-Averbakh, Stockholm Interzonal 1952,[1] Black (on move) would soon be forced to give up one of his rooks for White's c-pawn. He can, however, exploit the weakness of White's king-side pawn structure with 1... Rxc7! 2. Qxc7 Ng4! (threatening 3...Qh2#) 3. hxg4 Qf2+ salvaging a draw by threefold repetition with checks on h4 and f2. (See algebraic chess notation.)
In the diagram at right, from the classic game Hamppe-Meitner, Vienna 1872,[2] Black, having already sacrificed most of his pieces, forced a draw with 16..Bb7+! 17.Kb5! 17.Kxb7?? Kd7! 18.Qg4+ Kd6 followed by ...Rhb8# 17...Ba6+! 18.Kc6! 18.Ka4?? Bc4! and 19...b5# 18.Bb7+! 1/2-1/2.
A draw by perpetual check used to be in the rules of chess. However, it has been removed because perpetual check will eventually result in a draw by either threefold repetition or the fifty move rule. Also, if a player intends to draw the game in such a manner, the players usually agree to a draw.
Perpetual check can also occur in other chess variants, although the rules relating to it may be different. For example, giving perpetual check is not allowed (an automatic loss for the giver) in both shogi and xiangqi.
