Author: Bruce Moreland
Date: 18:16:53 12/18/02
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The idea behind null-move forward pruning is that you ask yourself, "Even if I give my opponent a free move, am I still winning if I let my opponent make a short search here?" If the answer is yes, you are probably winning pretty big, so you can discard this variation without doing long searches of all your legal moves. An example of this is if in a line you just took the opponent's queen, then the opponent made a nonsense move, if it was your move now you could ask yourself this question *now*. The answer would probably be, "I'm safe", so it would be safe to assume that the line is bad. In practice, a huge number of crap variations can be thrown away like this. You get into trouble when you are safe for the moment, but the computer has a longer term threat that you can't escape. The short depth null-move search won't detect the threat. You also get into trouble if you are in zugzwang, when the compulsion to move is what kills you. bruce
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