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July 14, 2005

The Concept of Zugzwang

Zugzwang, best translates from German as “compel to move”. Normally, being able to move is a good thing, for it comes along with choice - to defend, to attack, to do whatever you want; however, at times, it can be quite disastrous! In Zugzwang, all choices are bad moves, so the player would rather not play a move at all (null move). In other words, all paths lead out of Rome. Zugzwang typically occurs in the endgame when there are a few pieces left on the board.

Chess engines often deploy a “null move” heuristic, which essentially is based on the assumption that in a reasonable position, a move is better than a “no move”. It effectively allows the computer to consider one less ply. While the null move itself is illegal, the position after it must be legal with the opponent’s turn, i.e the king cannot be left in check. In order to avoid a null loop, a chess engine does not consider a null move if the previous move in the search was also a null move. Usually, chess engines also filter out positions with a low number of pieces to avoid Zugzwang.

Players often think along those lines to gain perspective from the opponent’s side of the board - “What is my opponent thinking? What is he trying to do?” The null move heuristic does not work in every game. For example, in checkers, any reasonably advantage is usually gained because of Zugzwang.

Posted by Oleg Ivrii at July 14, 2005 06:47 PM


I'm sorry Oleg, but you must now die.

Its for your own safety.

Peter will soon be joining you.

Posted by: HarGi at August 1, 2005 11:31 PM

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