jann wrote:
Gérard TAILLE wrote:
jann wrote:
This is a longstanding question in J89 which has two possible answers:
- Maybe passing for each ko is only required once for each player (see here)
- Or the problem was overlooked by J89 authors, and will be fixed in the future (with some hack like requiring a normal pass of either player before passing for a ko a second time)
1)
If you use "pass once per ko" then black can pass immediatly and wins the game because the two white marked stones are dead in the confirmation phase
2)
- Click Here To Show Diagram Code
[go]$$B
$$ +---------------------–-
$$ | 2 X X O X O . . . O X O . O . |
$$ | X O 1 O X O . . . O X X O O O |
$$ | O O X X X O . . . O X . X O X |
$$ | O X X O O O . . . O X X X X . |
$$ | . O X O . . . . . O O O O X X |
$$ | . O X O . . . . . . . . O O O |
$$ | O X X O . . . . . . . . . . . |
$$ | O O O O . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . |[/go]
without using "pass once per ko", in order to win, black must continue at least one move.
After
![white 2 :w2:](./images/smilies/w2.gif)
then black passes and wins the game.
Nice position, thank you. Even if harmless here since the result is the same (B can force the reinforcement with the same play either way), this does show a case where the attacker might need to play the same ko twice in confirmation.
I like challenge and, for fun, I tried to find a position with different result.
I believe the following one works.
- Click Here To Show Diagram Code
[go]$$B
$$ ---------------------------------------
$$ | . . . . . O . O . . O O X . X O . . . |
$$ | . . . . . O O X O O X O O X X O . O . |
$$ | . . . . . . O X X X X . X . X O . . . |
$$ | . . . , . . O O O O X X X X O O O O O |
$$ | . . . . . . . . . O O O X X X O X X X |
$$ | . . . . . . . . . . . O X . X X . X . |
$$ | . . . . . . . . . . . O O X X X X O X |
$$ | . . . . . . . . . . . . O O O X . O O |
$$ | . . . . . . . . . . . . . . O X X X O |
$$ | . . . , . . . . . , . . . . O O X O . |
$$ | O O O O O O O O O . . . . . . O X O . |
$$ | X X X X X X X X O . . . . . . O X X O |
$$ | X X X X X X X X O . . . . . . O O O . |
$$ | X X X X X X X X O . . . . . . . . O O |
$$ | X X X X X X X X O . . . . . . . . . . |
$$ | O X X , X X X X O , . . . . . , . . . |
$$ | . O X X X X X X O . . . . . . . . . . |
$$ | O O O X X X X X O . . . . . . . . . . |
$$ | . O X . X X X X O . . . . . . . . . . |
$$ ---------------------------------------[/go]
Let's call J89-ko-pass the J89 rule with the ko-pass instead of the pass-for-ko
Let's call J89-pass-once-per-ko the J89 rule with the pass-once-per-ko instead of the pass-for-ko
Assume that black will win the game by 0.5 points if white adds three moves in normal play to kill the black stones in the upper right corner.
- Click Here To Show Diagram Code
[go]$$B
$$ ---------------------------------------
$$ | . . . . . O W O . . O O X . X O . . . |
$$ | . . . . . O O X O O X O O X X O . O . |
$$ | . . . . . . O X X X X . X . X O . . . |
$$ | . . . , . . O O O O X X X X O O O O O |
$$ | . . . . . . . . . O O O X X X O X X X |
$$ | . . . . . . . . . . . O X . X X . X . |
$$ | . . . . . . . . . . . O O X X X X O X |
$$ | . . . . . . . . . . . . O O O X . O O |
$$ | . . . . . . . . . . . . . . O X X X O |
$$ | . . . , . . . . . , . . . . O O X O . |
$$ | O O O O O O O O O . . . . . . O X O . |
$$ | X X X X X X X X O . . . . . . O X X O |
$$ | X X X X X X X X O . . . . . . O O O W |
$$ | X X X X X X X X O . . . . . . . . O O |
$$ | X X X X X X X X O . . . . . . . . . . |
$$ | O X X , X X X X O , . . . . . , . . . |
$$ | . O X X X X X X O . . . . . . . . . . |
$$ | O O O X X X X X O . . . . . . . . . . |
$$ | . O X . X X X X O . . . . . . . . . . |
$$ ---------------------------------------[/go]
What is the point? Assume white has added the two marked stones before stopping the game.
In J89-ko-pass the upper right black group is dead => white wins the game => in normal play black must force the NO RESULT
In J89-pass-once-per-ko black group is alive by:
- Click Here To Show Diagram Code
[go]$$W
pass once for ko at 3
$$ ---------------------------------------
$$ | . . . . . O W O 5 7 O O 8 3 X O . . . |
$$ | . . . . . O O X O O X O O X X O . O . |
$$ | . . . . . . O X X X X 2 X 4 X O . . . |
$$ | . . . , . . O O O O X X X X O O O O O |
$$ | . . . . . . . . . O O O X X X O X X X |
$$ | . . . . . . . . . . . O X . X X . X . |
$$ | . . . . . . . . . . . O O X X X X O X |
$$ | . . . . . . . . . . . . O O O X . O O |
$$ | . . . . . . . . . . . . . . O X X X O |
$$ | . . . , . . . . . , . . . . O O X O . |
$$ | O O O O O O O O O . . . . . . O X O 1 |
$$ | X X X X X X X X O . . . . . . O X X O |
$$ | X X X X X X X X O . . . . . . O O O W |
$$ | X X X X X X X X O . . . . . . . . O O |
$$ | X X X X X X X X O . . . . . . . . . . |
$$ | O X X , X X X X O , . . . . . , . . . |
$$ | . O X X X X X X O . . . . . . . . . . |
$$ | O O O X X X X X O . . . . . . . . . . |
$$ | . O X . X X X X O . . . . . . . . . . |
$$ ---------------------------------------[/go]
and black cannot be killed because black managed te recreate the moonshine life loop wih three ko.
=> in normal play white must add a third move => black wins the game