Okay, an odd question, but it came up in Go club last week.

There is a ko on the board.

White takes the ko.

Black has no ko threat and passes.

White passes and the game ends.

Does white count Point A as territory, or is it dame?

Click Here To Show Diagram Code

[go]$$Bc Unfilled Ko
$$ ------------------
$$ | . . . . . . . . .
$$ | . . . . O . . . .
$$ | O O O O a O O O O
$$ | X O X X O X X X X
$$ | X X . . X . . . .
$$ | . . X X . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .[/go]

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The Witches of Castle Crabapple

I believe it dame
W has won an extra point by capturing the b stone

If it is AGA rules, white lost a point by giving black a stone when he passed.

Do you ask for a specific ruleset (which) or do you want to know the answer for all existing rulesets...?

Why is that "losing a point"? The pass stones merely allow an alternative counting of the otherwise constant area score. In particular, if the game is resumed, White fills, Black passes, White passes, then White has still made the last pass.

First thing to note is that passing does not lift a ko ban (or rather "should not").

Then, the outcome would be that White can fill that point anytime, so you should score it as such (or resume the game to the same effect).

Of course, technicalities of certain rulesets might make this more complicated.

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A good system naturally covers all corner cases without further effort.

Since 1949 the Japanese rules have said that the open point in the ko is not territory. Under the 1989 rules it is complicated. The ko stone in atari is dead, unless White reopens play. But if White does, Black gets to go first, and will take back the ko. So White should fill the ko before the end of play.

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Sheik Yerbuti -- if that really is your name --

Thanks, Bill, that's what I wanted to know. And thanks everyone else for the input!

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The Witches of Castle Crabapple

It does in Ing rules, it does in Japanese rules, it did in Shimada's rules and Yasunaga's rules, and it does in my rules. It is true that with multiple kos you may need a rule to prevent endless repetition after a pass, but that is doable, and has been done.

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Sheik Yerbuti -- if that really is your name --

So you want to know the ruling under current official (Nihon Kiin) Japanese rules? If the game is scored in your current position:

The ko stone is dead (the hypothetical ko rules do not alter that in hypothetical analysis). Therefore the adjacent empty intersection is not surrounded by live stones of one player. Therefore that intersection is dame (i.e., not territory). The ko stone is dead but not inside territory; therefore Black cannot remove it as part of the scoring. (If he wants to remove, he needs to do so in alternating play.) White's group (other than the ko stone) is adjacent to dame, therefore the group is (by definition of the rules) in-seki. Groups in-seki do not have any territory. Therefore White should have filled the ko in alternating play, i.e., BEFORE scoring. However, if White has made the mistake not to dissolve it, then the aforementioned consequences apply (and resumption or reconfirmation are further complications).

http://home.snafu.de/jasiek/rules.html
http://home.snafu.de/jasiek/j1989c.html

Yipes. Okay, moral of the story is: fill the darn ko. Got it.

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The Witches of Castle Crabapple

under aga rules, to my understanding (which is what i usually play), that would not be a point,
it would simply be an unfilled "dame". a point is defined as an empty intersection that is completely surrounded and cannot be taken away by the opponent. since that point can be taken away by resumption of play, it's not counted.

Under AGA rules, unless B disputes that e16 is alive, it is a point for W because it is entirely surrounded by live stones of a single color.

That said, W would have done well to play e17 instead of passing; it prevents the issue from coming up, and because of how the AGA rules work, it costs W nothing to do so.

See AGA rules here, particularly points 12 and 11.

Just to make things a little more confusing....under AGA rules (any area scoring rules acutally), if you have enough ko threats, it might be to your advantage to actually fill dame before playing out the ko.

A quick and dirty example:

Click Here To Show Diagram Code

[go]$$Wc White to play and win (no captures, 7.5 komi)
$$ ------------------
$$ | X O . . . . . . .|
$$ | X O . . . . . . .|
$$ | X O O . O . . . .|
$$ | X X O O . O O O O|
$$ | . . X X O X X . O|
$$ | . X . . X X . X O|
$$ | . . . . . . . X O|
$$ | . . . . . . . X O|
$$ | . . . . . . . X X|
$$ ------------------[/go]