[computer-go] Re: double threats

["Jens Lieberum" <jenslieberum@xxxxxxxx>]

Thank you very much for the very helpful answers. There remain some minor
details, that are not clear to me yet.

Anders Kierulf wrote:
>  Currently, it deems a block to be important if it's either:
> - 3 stones or more, or
> - surrounded by multiple chains (a likely cutting stone), or
> - adjacent to an unsettled group.

I do not understand exactly what it means to be adjacent to an unsettled
group. Typically, block tactics are done before groups are determined.
Or does group mean what I called block? In that case, it is also difficult
to have the actual status of adjacent blocks available. Probably, you do not
determine the status of blocks in more than one pass. Of course, you could
guess some status depending on the block status in the preceding position.


David Fotland wrote:
> First I do a search with W to move first, W wins all kos, and B must
answer
> all nearby threats.  If the
> search returns dead, then the group is dead.
>
> If the group is not dead, I repeat the search, with B to move first, B
wins
> all kos, and W must answer nearby
> threats.
>
> If this search returns stable, then W is stable.
>
> Otherwise, I repeat the search with B to move first, W wins all kos, and B
> must answer nearby threats.
> If this third search finds the group is dead, then it is unsettled, else
it
> is a ko or possible unsettled, and
> needs full board quiescence search.

There remains the (maybe unlikely) case of an unsettled block where a search
with W to move first, B wins all kos and W must answer nearby threats would
return "dead". In this case the status should be "special unsettled" as
well. Does the additional time to determine this status exactly not
sufficiently pay off in playing strength?

I see a problem, when a "special-unsettled" block belongs to a group that is
dead anyway. Maybe, this dead group will remain on the board for a long time
and will be the objective of a quiescence search in every evaluation. So
your solution requires that the block tactician does a very good job. For
example, the block tactician should be able to see that all blocks of a
surrounded group with a single eye and a ko are dead - no matter who is the
ko winner. Or alternatively, a group analyzer should be able to change the
status of blocks from "special-unsettled" to "dead" before starting the
quiescence search.

Jens Lieberum


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