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Subject: Re: Confusion on Null Move

Author: KarinsDad

Date: 22:54:25 02/09/99

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On February 09, 1999 at 22:59:52, Robert Hyatt wrote:

>On February 09, 1999 at 20:09:12, KarinsDad wrote:
>one of the big 'time savers' is what happens _below_ a sacrifice for nothing.
>Qxp pxq.  And now no matter what two moves white plays in a row, black's
>position is still 'good' and everything below such moves gets trimmed away

Ok. So in a given position (ply 0), there may be 5 captures (maybe even 10) that
are real losers (ply 1). For each of these, I would quickly find a response (ply
2, e.g. pxq). To do a null move, I would have to check about 36 reponses (on
average, not endgame) by white followed by 36 responses by white (i.e. all legal
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
that black cannot move out of check before the "ply 4" null move? Do you just
ignore it?

In a situation without the check (not knowing the answer yet), you pruned 10
lousy moves (although there was no guarantee that qxp, pxq didn't lead to mate
in 3 or more) and there are 26 left which are also null prune checked, but they
do not fail, so their children can be searched and pruned normally. Correct?


>IE with a full-width search, there are _many_ captures that are losers.  Null
>move reduces the depth below these moves and make dismissing them quick and
>>KarinsDad :)

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