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.
In the diagram on the right, from Unzicker-Averbakh, Stockholm 1952, with Black to play, it is clear that Black must 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! 3. hxg4 Qf2+ salvaging a draw by threefold repetition with checks on h4 and f2. (See algebraic chess notation.)
Perpetual check can also occur in other chess-like games, although the rules relating to it may be different. For example, giving perpetual check is not allowed in shogi.
See also
