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Subject: Re: Confusion on Null Move

Date: 10:06:35 02/10/99

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```On February 10, 1999 at 03:50:00, Peter McKenzie wrote:

[snip]
>
>Ok, so far we have :
>Ply 1. Q moves somewhere stupid,
>Ply 2. pxQ
>
>You then talk about doing a null move, but it is not clear to me when you want
>the null move to be done.  In this line, I think the important null move will
>come at ply 4.  So we might have:
>
>Ply 1 (white) Q moves somewhere stupid,
>Ply 2 (black) pxQ
>Ply 3 (white) try all moves here
>Ply 4 (black) try Null Move first (then try other moves)
>Ply 5 (white) try all moves
>Stop HERE if doing a 7 ply search (using R=2).
>
>So with any luck, the Null Move at ply 4 will hardly ever be refuted which means
>that in that branch you save yourself a whole **2 plies** of searching.

This is why I was typing in Ply 1, 2, etc. When someone charts it like this, it
is really easy to understand. Thanks a lot Peter. This helps immensely.

>
>I personally think that Null Move Pruning is the most significant computer chess
>algorithm to have been discovered in the last 10-20 years.
>
>>moves at ply 3 and all legals moves as if it was still white's move at ply 4)
>>for a total of 36 + 1296 or 1332 generated legal moves (37 calls of the legal
>>move generator) and 1332 evaluations (but possibly not a full evaluation).
>>
>>If any of the "ply 3" or "ply 4" null moves lead to check, do you have to search
>>on? And what do you do with the "ply 3" check where you are doing null move, so
>
>You don't try the null move if you are in check, does this answer your question?

Yes.

>
[snip]