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 Post subject: What is Anti-Seki?
Post #1 Posted: Thu Dec 19, 2019 7:41 pm 
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In the J89 rules, there's a curious position mentioned in the commentary:

Click Here To Show Diagram Code
[go]$$B Anti-Seki
$$ -------------
$$ | X O M X O .
$$ | . X X X O .
$$ | X X O O O .
$$ | O O O , . .
$$ | . . . . . .[/go]

which is explained as:
Quote:
If the game ends like this, Black and White are both dead but none of the stones can be removed. According to Article 8 there is no territory. Compared with playing X, Black loses 3 points.

How does this logically follow from the articles?
Why is the position not just a potential "both players lose" situation?
Is it because there are both black stones AND a white stone that could die (which makes it different than a both players lose where only stones of one color is unsettled)?
Is it because it involves a ko? However, the rules don't mention that as an explicit requirement nor talk about the existence of ko threats elsewhere.

Is this concept meant to generalize?
Would the below examples be considered anti-seki or just potentially "both players lose"?

Click Here To Show Diagram Code
[go]$$B Is this Anti-Seki?
$$ -------------
$$ | O . . X O .
$$ | X X X X O .
$$ | O O O O O .
$$ | . . . , . .[/go]

Click Here To Show Diagram Code
[go]$$B Is this Anti-Seki?
$$ ------------------
$$ | . . X O . O X .
$$ | . . X O . O X .
$$ | X X X O . O X .
$$ | O O O O O O X .
$$ | X X X X X X X .
$$ | . . . . . . . .[/go]

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 Post subject: Re: What is Anti-Seki?
Post #2 Posted: Thu Dec 19, 2019 11:11 pm 
Tengen

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Anti-seki means that both the black stones ARE dead and the white stones ARE dead (not: "could be dead"). Your examples show anti-sekis. The simplest anti-seki is two (large) strings sharing one liberty. In examples with kos, the (hypothetical) ko rules are also relevant for whether something is anti-seki.

If the players apply the tournament-like rule of both losing, they still apply the other rules about life and death to identify anti-seki and therefore existence of at least one effective move. However, multiple anti-sekis on the board (such as an anti-seki and its colour-reversed anti-seki elsewhere on the board) can mean that effective moves do NOT affect the result of the game...!

For J89 interpretation, read carefully enough to completely understand

http://home.snafu.de/jasiek/j1989c.html
http://home.snafu.de/jasiek/j2003.html
http://home.snafu.de/jasiek/j2003com.html
http://home.snafu.de/jasiek/rules.html

Also note that the two official J89 commentaries are totally insufficient to explain J89 and are partly wrong. Therefore, stop only referring to "the" J89 commentary.

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 Post subject: Re: What is Anti-Seki?
Post #3 Posted: Fri Dec 20, 2019 12:32 pm 
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Thanks for the response and clarifications!

So, I guess what you are saying is that a position can be both anti-seki and cause both players to lose, if it also creates an effective move that will affect the outcome.

I was under the mistaken impression that anti-seki vs both players lose were mutually exclusive.

What are the "two official" commentaries on the J89 rules?

I am only aware of the commentary that appears on the second half of this page:
https://www.cs.cmu.edu/~wjh/go/rules/Japanese.html

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 Post subject: Re: What is Anti-Seki?
Post #4 Posted: Fri Dec 20, 2019 12:41 pm 
Tengen

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These.

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 Post subject: Re: What is Anti-Seki?
Post #5 Posted: Fri Dec 20, 2019 11:35 pm 
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YeGO wrote:
In the J89 rules, there's a curious position mentioned in the commentary:

Click Here To Show Diagram Code
[go]$$B Anti-Seki
$$ -------------
$$ | X O M X O .
$$ | . X X X O .
$$ | X X O O O .
$$ | O O O , . .
$$ | . . . . . .[/go]


Why is the position not just a potential "both players lose" situation?


1. If the game completely ends with this shape remaining, it will be an anti-seki. (How is that possible? see item 3.)

2. Let us assume that both players were willing to touch this corner but they simply forgot to do so before the game stops by two passes.
The current Japanese rule expects that at least one player will ask "resumption of game" which means the opponent can play the first move. If i) both players declines to do such a request, and ii) they also don't want to end the game leaving this corner as an anti-seki, both players lose.
i) and ii) are the conditions for both players to lose.

3. I guess your real question is how anti-seki can remain on the board if two players are reasonable. Such a situation is possible by the following scenario.

Assume Black has many ko threats. White knows that it is hopeless to try to win this ko, but after careful counting, he realizes that he can win the game by 0.5 points if Black plays at X and finish the game. So White passes expecting Black to play at X. Now Black doesn't want to lose, thus he also passes, claiming that he has 4 points at this corner, not 3 points.

This is clearly different from the situation in item 2 where something is left by mistake. They intentionally chose this strategy and they are not willing to make a reinforcement even when one's opponent asks for the resumption of the game.

Unfortunately to Black, Black has the right to leave this shape and end the game, but he cannot collect 4 points because of the anti-seki rule. In this case, the rulemaker is secretly shouting Black that "You can't gain one point by not playing at X, so play at X!".

_________________
Jaeup Kim
Professor in Physics, Ulsan National Institute of Science and Technology, Korea
Author of the Book "Understanding the Rules of Baduk", available at http://home.unist.ac.kr/~jukim/index.php?mid=notice&document_srl=752233


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