Re: [gnugo-devel] PATCH: Marginal eye points with opponent stones in eyes.db

[Gunnar Farneback]

Dan wrote:
> There's nothing in those two tests which require marginal eye 
> spaces to be allowed to be occupied G5 would be parsed as
> (!.) warranting one half eye, while L10 would be parsed as (!) .

Then you know something about the optics algorithms that I don't know.
I thought tactically dead stones would always count as part of the
eyespace. Is that wrong?

> OOOOOX         OOOOOXX         OOOOXX
> O..XX.         O..XXO.         O..XO.
> ------         -------         ------
> 
> The first is a half eye, the second a full eye, the third
> a half eye. In the old scheme each of these would be parsed
> as (.!) .
> 
> If I understand correctly, these are to become (.!)  (..X$) and
> (..$). Thus they can be distinguished.

No, the X stones in the two last cases are tactically critical and
count as lunches, not eyespaces. This is problematic, but noone has as
yet proposed to change this.

> As far as I know the only issue that can't be dealt with in
> the old scheme have to do with the fact that if three stones
> are captured on the margin of an eye space then an eye results.

There are more. Just to give an example, this eyespace

OOOOOXX
O..X.O.
-------

is of the form "..X!". The abstract local game would be evaluated to 1
eye, and this is also what eyes.db, pattern 415, says. However, in the
real position above, O can make two eyes.

/Gunnar