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Subject: Re: Crafty-IsiChess,CCT4,r11 ==> A move to avoid?

Author: Gerd Isenberg

Date: 16:07:02 01/29/02

Go up one level in this thread


On January 29, 2002 at 18:13:47, Miguel A. Ballicora wrote:

>On January 29, 2002 at 16:54:20, Dann Corbit wrote:
>
>>On January 29, 2002 at 16:43:28, Roy Eassa wrote:
>>
>>>On January 29, 2002 at 16:36:23, Thomas Mayer wrote:
>>>
>>>>Hi Roy,
>>>>
>>>>>>Wow, Fritz 7b is blind to this one.  It does not see in advance that 37...Nxe5
>>>>>>is good for Black (it thinks Black is down more than 3 pawns).  Must be
>>>>>>null-move / zugzwang, right?
>>>>>
>>>>>
>>>>>To be more specific, in the following position Black can play ...Re6 and be in
>>>>>very good shape (certainly not behind).  However, Fritz 7b evaluates this
>>>>>position as being better for White by about 5 pawns:
>>>>>
>>>>>[d] 8/8/1p1r1k2/p1pRN1p1/P3K1P1/1P6/8/8 b - - 0 2
>>>>
>>>>strange... Quark fully disagrees and thinks that black is little bit better...
>>>
>>>
>>>Quark is right.  Fritz is wrong.
>>>
>>>I guess this is a very good example of a blindness caused by using null move.
>>>
>>>My question is, do all zugzwang positions confound null move, or only some?
>>
>>Since Thomas uses NULL MOVE in Quark, it makes you wonder what could be causing
>>the blind spot for Fritz?  Using it past the time when it is appropriate
>>perhaps?
>
>It depends on the implementation, I guess. Gaviota uses nullmove but it
>has no problem to see that Re6 is not winning for white and soon it sees
>that it is good for black by a small margin. In other words, it sees that the
>knight falls. Gaviota does not prune after nullmove, it reduces depth.
>So, zugswang problems are delayed only 2 plies.
>

I think that is, what Rainer Feldmann introduced as "Fail-High Reductions" in
Advances in Computer Chess 8. I also tried it in the Dos-IsiChess for a while.
Today a use a verification search, to confirm a NullMove Fail-High or to detect
Zugzwang. I think similar to Vincent's double NullMove.

Gerd



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