Author: Robert Hyatt
Date: 06:25:36 01/15/03
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On January 15, 2003 at 06:12:23, David Rasmussen wrote: >Since null moves are illegal in the real game, it is not obvious how it affects >or should affect repetitions and the fifty move rule. >What I do now in Chezzz is just pretty much ignore the relation between these >concepts and formulate them as if they were formulated in isolation. >What is the correct way to deal with these things? >For instance: 1. Update your hash signature to reflect the fact that a null-move has been played. Now the hash signatures will be different and you won't be matching with signatures _before_ the null-move and screwing things up. > >1. What to do with the fifty moves rule counter when doing a null move? I don't do a thing in this case... >2. When doing a null move, we obtain a new position, one that can never be > on the board immedeately after the currect position in a real game, but > it is treated as a "normal" position. What if a "repetition" is found of > two of these "imaginary" positions in the current line? We would return a > draw (that is what I do, since I treat these positions as all others, as do > most programs I've seen, Crafty for instance). That is reasonable. If you get a two-fold repetition below a null-move, why would you _not_ consider that a draw? > >I understand the need for draw detection and I understand the benefits of null >move pruning, but I think they affect eachother in an unclear way. What do >others do, and is there a way that is *correct*, and why? > >/David
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