Re: [computer-go] citation

[Gunnar Farnebäck <gunnar@xxxxxxxxxxxxxx>]

Xavier wrote:
> >  . X X X X X X X . .
> >  . X O O O O O X X X
> >  . X O X X X O O O X
> >  X X O X . X O . O X
> >  X O . O X . X O X X
> >  X O O O X X X O X .
> >  X X X O O O O O X .
> >  . . X X X X X X X .
> >
> >Here white (O) dragon has two false eyes, but lives.
> >
> I really don't understand why this eyes are considered as false eyes.
> For me they are as proper as the ones in my example. Can you point where
> is my mistake.

It's a question of terminology. In the sense that the white dragon is
unconditionally alive and the eye points are unconditional territory
it's certainly fair to call them proper eyes.

However, in almost all situations it's more useful to analyze the
diagonal points of an eye and if the opponent controls too many (I'm
deliberately vague here) call it a false eyes and disregard it for
life and death determination purposes. In GNU Go code and
documentation this is called topological eye analysis (and does also
take into account halfeyes and ko-dependent eyes).

So the point of a double-headed dragon is that it has two eyes which
by local analysis look like false eyes but lives only because the
strings surrounding the eyes are connected in a specific way.

/Gunnar
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