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Subject: Re: illegal positions in nalimov tablebases

Author: Tony Werten

Date: 02:17:28 02/04/05

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On February 04, 2005 at 04:15:26, Uri Blass wrote:

>On February 04, 2005 at 04:05:52, Tony Werten wrote:
>
>>You'll find lots more with white bishop on A8 and black pawn on B7, sntm in
>>check etc.
>>
>>What's your point ?
>>
>>Tony
>
>You are right that I will find better examples.
>
>These examples are better because they are illegal also in FRC or alternatively
>illegal with 3 pieces
>
>B2K4/1p6/8/8/3k4/8/8/8 w - - 0 1
>
>B2K4/1k6/8/8/8/8/8/8 b - - 0 1
>
>The point is that it may be possible to reduce the size of the nalimov
>tablebases by having only legal positions(unfortunately I guess that only a
>small reduction is possible).

Ah, I see. No, I think you could get a big reduction, the problem is just how to
identify these positions (fast).
In the TBS files, there is a count of "broken positions" wich are the illegal
positions. Quite a big percentage for some files as you can see.

There are also a lot of positions that can only be reached by first giving away
a won or draw position. You want to get rid of these as well.

Even better, recognize the won positions and you don't need the tablebases at
all :)

Just kidding, you don't seem to get the idea of tablebases. They are just a
stupid way of enumerating all possible positions and their value.

Eugene did make his generator a bit smarter by taking out some of the realy
stupid/illegal stuff, but it's still a stupid enumeration. What you're talking
about is making them smarter, but that's more about recognizers rather than
tablebases.


Tony

>
>Uri
>
>Uri



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