Re: [gnugo-devel] owl testcase

[SP LEE]

> Evan wrote:
> > A simple owl testcase from a game today.
>
> A wonderful illustration why static eye analysis is so terribly
> difficult. The position in the lower right corner is this:
>
> . . X . O . . . . 8
> . O . X O . . . . 7
> . O X X X O . . . 6
> . O O X O O O O . 5
> . . . X X O X . O 4
> . O . X O O X . O 3
> . . O O X X . X X 2
> . . . . X . . . . 1
> L M N O P Q R S T
>
> The black eyeshape is of the type
>
>  h
> ....
>
> or if we expand the halfeye
>
>  !
>  .
> ....
>
> which indeed is worth 2 eyes and life. However, white finds an owl
> pattern to try to attack at R1 (only chance, of course). After that we
> might expect the eyeshape to turn into
>
>  !
>  .
> .X..
>
> (which is what the local game model requires) but that is not what
> happens. In this position
>
> . . X . O . . . . 8
> . O . X O . . . . 7
> . O X X X O . . . 6
> . O O X O O O O . 5
> . . . X X O X . O 4
> . O . X O O X . O 3
> . . O O X X . X X 2
> . . . . X . O . . 1
> L M N O P Q R S T
>
> black can no longer safely (in the tactical sense) play at S3 (white
> attacks at S1) so the topological analysis declares R2 to be a false
> eye, and we get the eyeshape
>
>  !
> .X..
>
> which is only worth one eye. Then of course, if black would try S1 the
> eyeshape unexpectedly transforms to
>
>  !
>  .
> .X .
>
> and two eyes.
>
> I think it's clear that correct eye analysis in cases like this would
> require reading. Two questions appear:
>
> 1. How do we find relevant moves to read without getting a too slow
>    analysis?
> 2. What data structure would be appropriate for reading?
>
> /Gunnar
>
> PS If a white stone is added at O1 in the original position, there is
> still no way for white to kill all black stones in the corner,
> although it requires an under the stones tesuji to save black.
>
>

I have tried to simplify the problem as attached, on 9x9 board.
Surprisingly, GG can solve the problem correctly. The situation is:

   A B C D E F G H J
 9 . . . . X . . . . 9
 8 X X . X X O . . . 8
 7 . . X O O O + . . 7
 6 O O X . . . . . . 6
 5 . . O O + . . . . 5
 4 . . . . . . . . . 4
 3 . . + . . . + . . 3
 2 . . . . . . . . . 2
 1 . . . . . . . . . 1
   A B C D E F G H J
While analyzing the problem "owl_attack A8", GG tried C9 and find a
following answer directly at B9. While in the real game, GG answers R1
with R2 during owl analysis due to pattern D1002. I have also tried to
change the positions a little, but still can't repeat the flaw as in the
real game. I hope someone with more knowledge of the static eye analysis
and patterns can find the reason of this. Thus, why is the pattern D1002
not matched on simplified board? And, why is the vital move not found in
the real game?

SP Lee


begin 666 t.sgf
M*#M'35LQ749&6S1=05!;<4=O.C N,5U35%LQ70I36ELY74A!6S!=2TU;-2XU
M75!76U=H:71E75!"6T)L86-K70H*.T);86)=.U=;861=.T);8F)=.U=;8F1=
M.T);8V-=.U=;9&5=.T);8V1=.U=;8V5=.T);9&)=.U=;9&-=.T);96%=.U=;
A96-="CM"6V5B73M76V9B73M"6UT[5UMF8UT[0EM="@HI
`
end