Re: [gnugo-devel] Latest news from the Olympiad

[SP lee]

> See the end of regression/games/olympiad2004/19x19/gnu-ind.sgf.
>
> The problem is in the lower left corner:
>
> 12 O O O O O X X . O O X
> 11 O X X X O O . X X X O
> 10 X X X X O . X X O O O
>  9 . X O X O O O X O X X
>  8 O X O O O X O O O X X
>  7 . X X X X X O . O O X
>  6 . . X . . X O O X X X
>  5 . X O X O O X X X X X
>  4 X O O + . . X O X O O
>  3 X O . O O . X O X O O
>  2 X O O . X . X O X X X
>  1 . O . X . . . . . . X
>    A B C D E F G H J K L
>
> Black playing first can of course win the semeai trivially by making
> two eyes with A7, A6, or A5. I think black E4 would also win the
> semeai, although not quite so easily.
>
> The problem is that white playing first is not entirely dead. If black
> tries to keep white dead, the combination of white A1 and A7, followed
> by D4, leads to a ko for the life and death of both. Black can
> sacrifice the A4 string to gain certain life but in that case white
> also lives, so it would be a failure.
>
> Also interesting is the variation W A6, B A5, W A7, leaving black with
> only one eye, but in this case black eventually wins the semeai. Still
> we would want the owl code to see this attack, so that the semeai code
> will get to analyze it too. The problem here, however, is that we have
> a case of "eyeshape with cutting point",
>
> 12 O O O O O X X . O O X
> 11 O X X X O O . X X X O
> 10 X X X X O . X X O O O
>  9 . X O X O O O X O X X
>  8 O X O O O X O O O X X
>  7 O X X X X X O . O O X
>  6 O . X . . X O O X X X
>  5 X X O X O O X X X X X
>  4 X O O + . . X O X O O
>  3 X O . O O . X O X O O
>  2 X O O . X . X O X X X
>  1 . O . X . . . . . . X
>    A B C D E F G H J K L
>
> which have troubled us a long time. GNU Go thinks black is locally
> alive in seki here, which of course is wrong. Paul, should we try to
> revive your old patch for this problem?
>
> Another thing to investigate here is that there seems to be some kind
> of persistent cache problem. When the position is loaded GNU Go wants
> to play black A5 to eliminate a combination attack related to the
> semeai, but that doesn't happen when replaying the full game.
>
> /Gunnar
>
>

I couldn't see the black's next move to win the semeai. It seems to me that
white has more liberties. The important thing is W:A1 is absolute sente and
black has only 5 liberties in total.


SP Lee