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Subject: Re: Nullmove: when to avoid it?

Author: Robert Hyatt

Date: 13:52:05 02/28/01

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On February 28, 2001 at 14:49:19, Miguel A. Ballicora wrote:

>On February 28, 2001 at 13:22:41, Robert Hyatt wrote:
>>On February 28, 2001 at 11:10:30, Miguel A. Ballicora wrote:
>>>On February 28, 2001 at 05:56:36, Leen Ammeraal wrote:
>>>>I am not sure about when to avoid nullmoves.
>>>>I omit it:
>>>>a. when in check
>>>>b. when there are less than 5 pieces (including pawns) on the board
>>>>c. when the last move was a nullmove
>>>>d. at the root node
>>>>Should I also omit it in some other cases,
>>>>for example, when any hashmove (even with a low draft) was found,
>>>>or when beta = alpha + 1?
>>>>Thanks in advance for any help.
>>>Hi Leen,
>>>Regarding b, I do not know whether what I am doing now is correct but I think
>>>that works for me:
>>>When either black or white had no "long range" pieces (bishop, rook or queen)
>>>I disable null move. The rationale is that one side cannot waste
>>>a tempo in a given position having pawns, king and/or knights making the
>>>position prone to have a zugswang.
>>That seems dangerous.  you are white, with a bishop on d5.  I am black and I
>>have a pawn on a7 and g7.  The bishop is zugged here.  If your king can't move,
>>you lose even though you have a long-range slider on the board.  And null move
>>will fail high here naturally as not moving is better than having to move and
>I think that you meant a3 and g3?

Sorry.  I am white, you are black trying to stop both of my pawns.

> If that's so I got your point
>and you're right. However, I disable nullmove when _either_ side lacks a
>long-range slider. In your example, it will be disabled because you do not
>have a bishop. If you do have a bishop, it won't be disabled (both sides got a
>slider) but at least I don't have "mutual" zugswangs which are the nastiest (I
>think). At least, with a slider per side the mutual zugswangs are more difficult
>(of course not impossible but I have to draw a line somewhere).

That only makes it worse.  So I have a bishop and two pawns threatening to
promote.  You have the bishop as above.  You are _still_ zugged.  I don't
see why you would limit null move based on _both_ sides.  You should only
limit it if the side on move can be zugged.  But in any case, it still fails
if we both have a bishop.


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