Author: John Coffey
Date: 10:01:01 09/28/98
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On September 28, 1998 at 09:32:12, Robert Hyatt wrote: >that's the point, however. There are practically *no* positions in chess where >playing two moves in a row wouldn't result in winning something. IE if we >played a game where I could make two moves in a row once, I'd expect to beat you >every time. In your case, you can't put your queen on a square where it can be >attacked in one move, because that's when I'll use my two moves, once to attack >it, once to rip it. You can't put your king on a square where I can attack and >then mate using two moves. > >In tree searches, this most commonly happens when one side is way down in >material and even giving him two moves in a row he can't regain enough to get >back to equal. > >In endgames, this doesn't work as well, because with no pieces on the board, >such double-move threats are less serious (they do exist, but we don't do null- >move when there are no pieces). If practically no positions in chess where making two moves in a row doesn't when something, then how do null move cutoffs reduce the size of the tree from 6^depth to 3^depth? Unfortunately there is still much confusion in my mind on how to implement these. What I gather from the previous discussion is that for every position we check a null move response and if the opponent's position does not improve then we make a cut off. It is hard for me to see why we would do this when down matieral? (i.e. people have said that they do this check "everywhere.") Seems to me that if down material then the next move could regain material. If we do a null move where we skip a move then chances are the opponent could win more material. I have asked repeatedly if we only do the null move check when up material, and I have been told repeatedly that it is done everywhere. How does one evaluate the null move? i.e. say we are up 9 points and we do a null move check and the result is that we are only up 4 points (the opponent gained a rook with the null move) Do we evaluate the position as +9 or +4? John Coffey
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