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

Author: Robert Hyatt

Date: 11:42:52 07/15/02

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On July 15, 2002 at 13:30:54, Gian-Carlo Pascutto wrote:

>On July 15, 2002 at 13:11:09, Christophe Theron wrote:
>>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.
>I think the idea is simply to show that you can nullmove and still
>have a correct search. (but only with double nullmove, not single)

I think the discussion is pointless, myself.  Null-move search is _not_
equlvalent to non-null-move search.  It demonstrably has more errors due to
reducing the depth on many sub-trees.

The concept of "correct search" is therefore so abstract as to mean absolutely
nothing.  double-null eliminates _some_ zugzwang problems, but not _all_.  It
is obviously impossible to eliminate all of them, particularly when you are
whacking 6 plies off the tree depth and then drawing conclusiong about the
resulting sub-trees..

The only useful definition of "correct search" would be to somehow prove
that a null-move search to depth=D would produce the _same_ move as a
non-null-move search to depth=D, for all positions.  This is simply not

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