Reciprocal Zugzwang
Hooper 1970, p. 21| a | b | c | d | e | f | g | h | ||
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| a | b | c | d | e | f | g | h |
A special case of zugzwang is reciprocal zugzwang or mutual zugzwang, which is a position such that who ever is to move is in zugzwang. Positions of reciprocal zugzwang are surprisingly important in the analysis of endgames (Nunn 1995:6), (Nunn 1999:7). A position of mutual zugzwang is closely related to a game with a Conway value of zero in game theory (Stiller 1996:175).
The diagram on the right shows a position of reciprocal zugzwang. If Black is to move, he must move 1... Kd7 and lose because White will move 2. Kb7, promote the pawn, and win. If White is to move, he must either move 1. Kc6 which is a draw because it stalemates Black or he must abandon the pawn, which is also a draw after Black captures the pawn. Both sides would be in zugzwang if it were their move, so it is a reciprocal zugzwang (Hooper 1970:21), (Averbakh 1993:35).
In a position with reciprocal zugzwang, only the player to move is actually in zugzwang. However, the player who is not in zugzwang must play carefully because one inaccurate move can cause him to be put in zugzwang (Müller & Pajeken 2008:179). That is in contrast to regular zugzwang, because the superior side usually has a waiting move to put the opponent in zugzwang (Nunn 1999:7).
Read more about this topic: Zugzwang
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