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We now consider an example to show why the komaster is reset
to EMPTY
if the ko is resolved in the komaster's favor. This
means that the ko is filled, or else that is becomes no longer
a ko and it is illegal for the komaster's opponent to play
there.
The position resulting under consideration is in the file regressions/games/ko5.sgf. This is the position:
. . . . . . O O 8 X X X . . . O . 7 X . X X . . O . 6 . X . X X X O O 5 X X . X . X O X 4 . O X O O O X . 3 O O X O . O X X 2 . O . X O X X . 1 F G H J K L M N
We recommend studying this example by examining the variation file produced by the command:
gnugo -l ko5.sgf --quiet --decide-string L1 -o vars.sgf
The correct resolution is that H1 attacks L1 unconditionally while K2
defends it with ko (code KO_A
).
After Black (X) takes the ko at K3, white can do nothing but retake the ko conditionally, becoming komaster. B cannot do much, but in one variation he plays at K4 and W takes at H1. The following position results:
. . . . . . O O 8 X X X . . . O . 7 X . X X . . O . 6 . X . X X X O O 5 X X . X X X O X 4 . O X O O O X . 3 O O X O . O X X 2 . O O . O X X . 1 F G H J K L M N
Now it is important the `O' is no longer komaster. Were `O' still komaster, he could capture the ko at N3 and there would be no way to finish off B.