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Subject: Re: Nullmove: when to avoid it?

Author: Miguel A. Ballicora

Date: 22:39:05 02/28/01

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On March 01, 2001 at 01:35:53, Miguel A. Ballicora wrote:

>On February 28, 2001 at 16:52:05, Robert Hyatt wrote:
>
>>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.
>>>>>>Leen
>>>>>
>>>>>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.
>>>>>
>>>>>Miguel
>>>>
>>>>
>>>>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
>>>>lose.
>>>
>>>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.
>
>The idea is to limit the nullmove when there is a zugswang that matters.
>In other words, there are zugswangs where it does not matter if I move or not.
>The example that you give could be one as pointed out by R. Gibert. If you move
>you lose because you are zugswang if you don't I win anyway advancing one of the
>pawns. Let me give an example trying to keep the spirit of your criticism
>so I can illustrate the idea:
>
>[D]2k5/1p6/1K5p/2p4P/2P5/1P2b3/8/4B3 w - - 0 1
>
>White plays Bg3 and Black is zugswang. Black king can move without losing a pawn
>and Bishop can move defending c5 and at the same time avoiding Bf4.
>This is not a mutual zugswang, because if white is on the move still win wasting

I meant CAN'T...

Miguel




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