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Subject: Re: What is exactly a Null Move ?

Author: Bruce Moreland

Date: 01:33:53 07/23/99

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On July 23, 1999 at 04:22:04, Tania Devora wrote:

>
>
>Somebody please explain me what is a Null Move ?
>
>Thanks for your help!

You have a position where it is your move and you are up a queen.  You can
search this position normally, which will take a while.

Or you can pretend that it is your opponent's turn to move, and let them take a
free shot at you via a shallower search.  If you are still up a queen at the end
of that, assume that you'll be up at least a queen if you move normally and
search to normal depth.

A "null move" is a move that doesn't change the position on the board, but just
changes the side to move.

It is used to achieve greater search depths by pruning out nonsense variations
where one side is ahead and the other has no counterplay.

This can fail becaus the null move isn't legal in chess, and sometimes you are
in zugzwang and are forced to wreck your position.

So this use of the null move to eliminate nonsense variation is not without
risk, because sometimes you miss tactics that involve zugzwangs or longer-term
threats that are inescapable.

bruce



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