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'm not very familiar with static eye analysis, but I don't understand
why GG needs move reading here. Can we just let GG know that T1 is a
potential eye because it's on the corner? The situation is similar to
the following:

  OOX.O.
  XX.XXX
  X....X

I'm not sure if GG can solve the above case.

SP Lee