Re: [gnugo-devel] Bug: gnugo plays inside own territory for no reason

[XUEPING LI]

> 
> Malcolm wrote:
> > For the attached sgf file, gnugo thinks that white should play N5:
> 
> This is the position:
> 
>   A B C D E F G H J K L M N
> 13 . . O X X X X O O O O . . 13
> 12 . . O O X O O O X O O O X 12
> 11 . O . O X X O X X X O O . 11
> 10 . . O X . X X X . X O . O 10
> 9 . . O X X X O . . . X O O 9
> 8 . O . O X O X X . . X X X 8
> 7 O O . O O O X . X + X X O 7
> 6 X X O O O O O X . O X O O 6
> 5 X X O . X X O X X O X O . 5     WHITE (O) has captured 5 stones
> 4 X O O X X O O O O X X O X 4     BLACK (X) has captured 4 stones
> 3 X X X X . X O X X O O O O 3
> 2 . . O O X . X . X X O . X 2
> 1 . . . . X X X X X O O X . 1
>   A B C D E F G H J K L M N
> 
> and according to the sgf file the game was played with Japanese rules.
> 
> > address@hidden:~$ gnugo --score finish -l Defner-pepsiman-
> 20041213.sgf> 136 white (O) move N5
> > 137 black (X) move D5
> > 138 white (O) move : PASS!
> > 139 black (X) move : PASS!
> > Black wins by 7.5 points
> > 
> > This gives black an extra point, so I think it has made a mistake.
> 
> No, N5 is correct. The lower right corner is a seki and under Japanese
> rules no points are awarded in seki for either player. Thus there is
> no territory at any of the points, N5, N4, M2, N2, M1, or N1. In fact
> white gains one point by playing N5. It's still a seki after the move
> so there is no territory but the captured stone at N4 now counts one
> point as a prisoner.
> 
> Under Chinese rules white should play D5 before N5. (I don't know if
> N5 is necessary in that case but it certainly doesn't hurt white.) 
> 
> /Gunnar
> 
> 

I do believe that N5 decreases white territory by 1 point in Japanese rule. 
Although it is seki in lower right corner, the white group has 3 points and the 
black group has 1 point. We could also imagine that the white group has a 
larger eye and captured 2 black stones and it is still seki. For example,

 8 . O . O X O X X . . X X X 8
 7 O O . O O O X . X + X O O 7
 6 X X O O O O O X . O X O . 6
 5 X X O . X X O X X O X O X 5     WHITE (O) has captured 5 stones
 4 X O O X X O O O O X X O X 4     BLACK (X) has captured 4 stones
 3 X X X X . X O X X O O O O 3
 2 . . O O X . X . X X O . X 2
 1 . . . . X X X X X O O X . 1
   A B C D E F G H J K L M N

However, now playing inside own territory will not decrease any point because 
black has to throw in again to keep it seki.


SP Lee