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Subject: Re: EGTB: Better algorithm

Author: Urban Koistinen

Date: 08:15:04 04/08/01

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On April 08, 2001 at 08:41:19, Uri Blass wrote:
>1)I tried to explain the paper in more words in order to understand it and the
>first part that I did not understand was the sentence:
>"t4 depends on t3 and d"
>It seems to me that t4 is dependent also on t1.
>
>Here is an example of position in t4
>
>[D]2k5/8/2K1Q3/8/8/8/8/8 b - - 0 1
>
>The position after Kb8 is in t3 but the position after Kd8 is in t1.

Any position in t1 is also in t3 and t(2n+1) because if a position is a win for
white with g50=x it is also a win for white with g50>x.

>I prefer not to try to understand the rest of the paper before I understand this point.
>
>2)Here is my explanation of the part that I did understand:
>
>I call capturing or pawn move in the same word conversion.
>
>tables ti are clear
>They include all the positions when it is a win for white but white need i plies to get the conversion.

For even i: ti is legal and a loss for black with g50=i
For odd i: ti is illegal or a win for white with g50=i
If white win with g50=i, white obviously win if g50>i.

>Table d include only legal positions that are not stalemate and black cannot
>save itself by conversion.

Include <=> value=1

>We want to find positions that are win for white.
>other positions are not intereting because it is obvious that they are not win
>for white.
>
>It is clear that t1 depends on t0 and previous tables that can be reached by a
>conversion(a position is in t1 only if white wins by conversion or by checkmate
>in 1 ply).
>
>t2 are positions when black is to move.
>The position is legal and black cannot save itself by conversion and it means
>that t2 is included in d.
>If black try to play a move that is not conversion it gets to position in t1 so
>it depends also on t1.
>
>t3 are positions when white is to move.
>White cannot win by conversion otherwise the position is in t1.
>White can get by a move that is not conversion to position in t2.
>
>This is the reason that t3 is dependent on t2 and t1.

Yes, t3 can be computed by computing: or(t1,max(reachable(t2))).

Urban Koistinen



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