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Subject: Re: Null-Move: Difference between R = 2 and R = 3 in action

Author: Vincent Diepeveen

Date: 08:01:23 07/16/02

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On July 15, 2002 at 13:11:09, Christophe Theron wrote:

>On July 15, 2002 at 08:37:34, Omid David wrote:
>>I don't think using double null-move is a good idea in practice, since in
>>midgame the chance of zugzwang is negligible and thus it's superfluous (I doubt
>>if even DIEP uses it). However the contribution of double null-move is that it
>>gives legitimacy to the null-move pruning idea, proving that it _is_ a correct
>>search method (anyway, no one doubts null-move nowadays).
>Why does double null move prove that null move is a correct search method????
>Doing two null moves in a row means going back to standard search (a search not
>involving an illegal move like null move is).
>I fail to see how it legitimates null move.

Double nullmove legitimates (duh can't you use easier to spell words)
itself, for the obvious reason that it is provable now that a search
depth of n ply, where i may pick n, is going to solve any problem you
give it.

Normal nullmove, if you remember the discussions a few years ago,
especially around 98 and 99, it was told to be an inferior way of
search, because for *any* selfpicked depth n for the nullmove search
it could conclude less than a small outdated fullwidth search, so was
the theory.

This is not true of course.

Reality is that only a few problems need a bit bigger search depth
with double nullmove, and most are far endgames.

In middlegame it's very seldom one needs 3 ply more than a fullwidth
search would get.

Note that getting a fullwidth search of more than 12 ply is impossible
whereas most get 14-15 ply with nullmove nowadays easily in tournament

DIEP's probably only exception here, it needs a supercomputer to get
that depth ;)

>    Christophe

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