Zugzwang is a position in which it is disadvantageous to move, as every move leads to a worse, and often lost position. Most of the time it happens in late endgames, specially pawn endings, the most obvious example being a KPK endgame, where opposition can be regarded as a special case of zugzwang.
Zugzwang and Null Move
Zugzwang positions are known cause the Null Move Pruning go wrong. For that reason most programs do not use null move in the late endings. As far as middlegame positions are concerned, programmers either assume that they happen too rarely to bother with them, or use some sort of verification pruning.
Mutual Zugzwang
Mutual or reciprocal zugzwang is a rare position such that who ever is to move is in zugzwang, which may occur in late endings [1].
Trébuchet
A Trébuchet is an extreme winning/losing type of reciprocal zugzwang in pawn endgames, also broached in Noam Elkies publication On numbers and endgames. [2].
Noam D. Elkies (1999). On numbers and endgames: Combinatorial game theory in chess endgames. pdf, differs only in trivial stylistic details from the (1996) version published in Games of No Chance edited by Richard J. Nowakowski
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Zugzwang is a position in which it is disadvantageous to move, as every move leads to a worse, and often lost position. Most of the time it happens in late endgames, specially pawn endings, the most obvious example being a KPK endgame, where opposition can be regarded as a special case of zugzwang.
Zugzwang and Null Move
Zugzwang positions are known cause the Null Move Pruning go wrong. For that reason most programs do not use null move in the late endings. As far as middlegame positions are concerned, programmers either assume that they happen too rarely to bother with them, or use some sort of verification pruning.Mutual Zugzwang
Mutual or reciprocal zugzwang is a rare position such that who ever is to move is in zugzwang, which may occur in late endings [1].Trébuchet
A Trébuchet is an extreme winning/losing type of reciprocal zugzwang in pawn endgames, also broached in Noam Elkies publication On numbers and endgames. [2].See Also
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