Re: [gnugo-devel] gnugo 3.4 problems

[Gunnar Farnebäck]

Dan wrote:
> Here's some variations. For B, ``chickening out'' means
> playing at E19, which he has the option of doing even
> after W wins the ko once or twice. After that, seki is the
> most probable outcome, since W can still try to kill, but at a
> price of (I think) ignoring two B tenukis, plus losing sente.
> The incentive to take the sente will be too strong for W to
> ignore.

That depends on the ko threat situation of course, although I agree
that the ko in most cases is too difficult to play.

It may also be worth looking at the variations starting with B:C19,
W:A14, B:G19, W:E19, B:J19, where black opens up a second ko. I don't
think it makes much difference in the end but it adds to the
complexity of the position.

> I think that indirect kos are quite common in semeai situations
> but less so where only one group is at stake, though there is
> the complication that there could be internal ko threats. If
> there is only one group, usually one fights a ko to gain an
> eye. Such a ko is direct since whoever wins it can immediately
> settle the issue.

That is not always the case. See for example ld_owl:177. We also have
at least one very good example in the regressions that I haven't
managed to locate. I'll keep an eye out for examples.

> But if there are two groups, there is another way kos can happen
> (like in this game) where one fights a ko to keep a liberty open
> while one tries to fill the opponent's liberties. These ``yose kos''
> seem special to semeai.

Semeai indeed has more potential for complex results, in particular
the positions where one or both players can choose between seki and a
ko for life and death of both.

> Do you have some examples that are not semeai where
> the KO_A, KO_B scheme is inadequate?

I'll keep an eye open. But remember that tactical reading also has a
need to understand small-scale semeais, which may very well include
complex ko results. For example the S19 move at the start of this
discussion was found by tactical reading.

/Gunnar