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Status question : is this a bent four in the corner?
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Author:  Actorios [ Sun Oct 28, 2012 10:22 am ]
Post subject:  Status question : is this a bent four in the corner?
Hello,
A friend of mine come up with the below pattern.

What is the status of the white group?
What is the result of a game where this pattern is present after both players pass?

Click Here To Show Diagram Code
[go]------------------
$$ | . X X . O X .
$$ | . O . O O X .
$$ | O O O O X X .
$$ | X X X X X . .
$$ | . . . . . . .[/go]


Many thanks in advance,
Author:  Sverre [ Sun Oct 28, 2012 10:25 am ]
Post subject:  Re: Status question : is this a bent four in the corner?
Quote:
What is the status of the white group?

It is a ten thousand year ko.
Author:  Bill Spight [ Sun Oct 28, 2012 10:36 am ]
Post subject:  Re: Status question : is this a bent four in the corner?
Click Here To Show Diagram Code
[go]$$
$$ ------------------
$$ | . X X . O X .
$$ | . O . O O X .
$$ | O O O O X X .
$$ | X X X X X . .
$$ | . . . . . . .[/go]


Several years ago I dubbed this "Simon's Ko" after Simon Goss, who brought it up on rec.games.go.

At the end of play it is, AFAIK, seki under all commonly used rules.
Author:  Actorios [ Sun Oct 28, 2012 10:43 am ]
Post subject:  Re: Status question : is this a bent four in the corner?
Thanks a lot to both for your prompt answer !
I thought that Black was at an advantage since he could make a bent four by ignoring 1 ko threat and connect while White would have to ignore 2 or 3 ko threats (depending on who takes first) to obtain the same result.
Author:  Bill Spight [ Sun Oct 28, 2012 10:53 am ]
Post subject:  Re: Status question : is this a bent four in the corner?
Generally Black does have the advantage. OC, the ko threat situation matters. But often Black should make a direct ko before the end of the game, even if he has to trade the ko for the value of the threat.
Author:  mitsun [ Mon Oct 29, 2012 11:36 am ]
Post subject:  Re: Status question : is this a bent four in the corner?
Click Here To Show Diagram Code
[go]$$ seki (not bent four)
$$ ------------------
$$ | X X X . O X .
$$ | X O . O O X .
$$ | O O O O X X .
$$ | X X X X X . .
$$ | . . . . . . .[/go]


Click Here To Show Diagram Code
[go]$$ ko (W captures first)
$$ ------------------
$$ | . X X . O X .
$$ | X O X O O X .
$$ | O O O O X X .
$$ | X X X X X . .
$$ | . . . . . . .[/go]
Author:  Bill Spight [ Mon Oct 29, 2012 12:26 pm ]
Post subject:  Re: Status question : is this a bent four in the corner?
Just a note on the normal Black advantage.

As Mitsun's diagram shows, it takes two moves for Black to make a direct ko, and then it would take White two moves to win the ko. The same goes if White makes a direct ko. So the territory value of the corner lies between -8 (if Black makes and loses the ko) and +20 (if White makes and loses the ko). With no ko threats, the correct outcome is 0 (seki). (Under some rules the seki would be worth +2, since Black gets two moves.)

OC, if either player has a sufficient number of large enough ko threats, it will be to their advantage to make the ko, or to Black's advantage to make seki by playing on the 1-1. But suppose that both players have ko threats, but neither player has enough big threats to win the ko outright. Each player would have to ignore the opponent's threat to win the ko. Then we may estimate the value of the corner as the average between -8 and +20, or +6.

That is just an estimate, of course, but it does tell us that there will be many times that Black will do better to make and play the ko instead of accepting seki. :)
Author:  cyclops [ Mon Oct 29, 2012 12:45 pm ]
Post subject:  Re: Status question : is this a bent four in the corner?
I admire your wisdom of couse but wouldn't it be more simple to observe that white has more to lose than black in this position?
Author:  shapenaji [ Mon Oct 29, 2012 3:13 pm ]
Post subject:  Re: Status question : is this a bent four in the corner?
EDIT: Ugh, today is not my day,

Black can, of course, still make seki in my diagram.

The red section is completely wrong.


Hmm, so this is interesting, so basically we have these eventualities:

1) White plays first, forcing it to become a ko
a) Black responds, white gets a direct ko
b) Black tenukis, white starts, black gets a direct ko

2) Black plays first and gets a seki

3) Black plays first and we're left with the same situation as in 1)

The important thing here is, either side can make a move to prevent it from ever becoming seki, but at the same time, creating something similar to a 10,000 year ko, ("similar" because even though each side is at a disadvantage, it can't be resolved with seki)

So, since black is at a huge advantage here. (White needs an enormous number of large threats).

Black plays and prevents it from becoming seki,

Click Here To Show Diagram Code
[go]$$ ko
$$ ------------------
$$ | . X X . O X .
$$ | . O X O O X .
$$ | O O O O X X .
$$ | X X X X X . .
$$ | . . . . . . .[/go]


Now, I think, if white has at least 1 more large threat (>=18) than black has small threats (>=8), white starts the ko. It is at least as good as seki for white.

What I'm curious about is:

Is there a resolution to this situation which involves both sides filling in all their ko threats?

I have this weird feeling that that might be the best resolution if the threats are close. Neither side wants to give the opponent the first move in the ko, if you start the ko, you lose it. So instead, you remove your opponent's best threat, then they're 1 behind, if they tenuki, you start the ko and gain off it.

You could make a problem here where there's another small ko somewhere on the board, and each side starts fixing their ko threats AS ko threats.
Author:  Magicwand [ Mon Oct 29, 2012 4:18 pm ]
Post subject:  Re: Status question : is this a bent four in the corner?
Bill Spight wrote:
Click Here To Show Diagram Code
[go]$$
$$ ------------------
$$ | . X X . O X .
$$ | . O . O O X .
$$ | O O O O X X .
$$ | X X X X X . .
$$ | . . . . . . .[/go]


Several years ago I dubbed this "Simon's Ko" after Simon Goss, who brought it up on rec.games.go.

At the end of play it is, AFAIK, seki under all commonly used rules.


i believe white is dead on japanese rule if left as it is.

but below shape is seki if black doesnt have any ko threat.
Click Here To Show Diagram Code
[go]$$
$$ ------------------
$$ | W X X . O X .
$$ | . O . O O X .
$$ | O O O O X X .
$$ | X X X X X . .
$$ | . . . . . . .[/go]


edit: correction.. if it is left alone..it is seki.

edit:
it is ko...but black need to have one more ko threat to win...
white need one more (big enough) ko threat to capture black.

if both decide not to play then it is left at below position and seki.
Click Here To Show Diagram Code
[go]$$
$$ ------------------
$$ | W X X . O X .
$$ | . O . O O X .
$$ | O O O O X X .
$$ | X X X X X . .
$$ | . . . . . . .[/go]
Author:  Uberdude [ Mon Oct 29, 2012 5:03 pm ]
Post subject:  Re: Status question : is this a bent four in the corner?
It so happens I actually made this shape (as white, due to my own suicidal/masochistic tendencies, I decided not to easily live for some bizarre reason) at the Brussels tournament this weekend and it became the ko. I'll post the game once I've recorded it.
Author:  mitsun [ Mon Oct 29, 2012 6:42 pm ]
Post subject:  Re: Status question : is this a bent four in the corner?
Bill Spight wrote:
Just a note on the normal Black advantage.

As Mitsun's diagram shows, it takes two moves for Black to make a direct ko, and then it would take White two moves to win the ko. The same goes if White makes a direct ko. So the territory value of the corner lies between -8 (if Black makes and loses the ko) and +20 (if White makes and loses the ko). With no ko threats, the correct outcome is 0 (seki). (Under some rules the seki would be worth +2, since Black gets two moves.)

OC, if either player has a sufficient number of large enough ko threats, it will be to their advantage to make the ko, or to Black's advantage to make seki by playing on the 1-1. But suppose that both players have ko threats, but neither player has enough big threats to win the ko outright. Each player would have to ignore the opponent's threat to win the ko. Then we may estimate the value of the corner as the average between -8 and +20, or +6.

That is just an estimate, of course, but it does tell us that there will be many times that Black will do better to make and play the ko instead of accepting seki. :)


B can choose between seki and ko, while W has no way to make seki or to prevent B from making ko, so B is in the driver's seat. Let's assume B is considering whether to start the ko (which he plans to win) or leave the position alone. The point spread is 0 (leave as seki) to +16 (start and win ko). The move spread is 0 (leave as seki) to 3 (start and win ko). Since it takes B three moves to make 16 points, W only needs to play gote moves worth 5-6 points to break even. It will not be profitable for B to start the ko until pretty late in yose, even if he has lots of large threats.

(As a side note, I do not know much about the concept of "temperature" in Go, but it seems like the first B approach move does nothing but heat the corner, since it now takes either side only two moves to start and win the ko. The price B pays to raise the temperature is the value of a W gote move.)
Author:  RobertJasiek [ Mon Oct 29, 2012 10:10 pm ]
Post subject:  Re: Status question : is this a bent four in the corner?
Magicwand wrote:
Bill Spight wrote:
Click Here To Show Diagram Code
[go]$$
$$ ------------------
$$ | . X X . O X .
$$ | . O . O O X .
$$ | O O O O X X .
$$ | X X X X X . .
$$ | . . . . . . .[/go]



i believe white is dead on japanese rule if left as it is.


Suppose "left as it is" shall mean "still exists on the board after the first succession of two passes" and "japanese rule" shall mean "current official Japanese Rules of the 1989 kind". Then each string is alive.

White is alive because Black's only interesting chance of attack is via throw-in to make ko, which White captures first (he passes until the non-ko string is in atari). Then Black is, by the rules, required to ko-pass before he may recapture. So White dissolves the ko before Black may recapture.

Black is alive because the same argument with inversed colours applies to the small black string.

Quote:
but below shape is seki if black doesnt have any ko threat.
Click Here To Show Diagram Code
[go]$$
$$ ------------------
$$ | W X X . O X .
$$ | . O . O O X .
$$ | O O O O X X .
$$ | X X X X X . .
$$ | . . . . . . .[/go]



Under the assumptions above, the aforementioned reasoning applies to the corner's non-ko-strings. The interesting string is the ko string. Black's only interesting chance of attacking it is to start by capturing it. Then White ko-passes. Then Black chooses to fill the ko. then White does not have any successful local possibility to establish a permanent stone. This circumstance requires more precise interpretation of the 1989 Rules.

The Japanese 1989 Rules themselves leave it unclear what exactly "enable" means and whether a remote permanent stone would be a valid form of enabling.

It requires the Japanese 2003 Rules as interpretation aid for the Japanese 1989 Rules to clarify the locality. In short, it is restricted to the corner's locale. Since, after the mentioned sequence, White cannot get a local-1 or local-2 permanent stone, the ko stone is dead.

None of the corner's empty points is an eye-point; they are dame. Therefore the situation is in-seki (informally "a seki"). Groups in-seki do not have territory, so the dead white ko stone may not be removed. The local score is 0.
Author:  Magicwand [ Tue Oct 30, 2012 4:56 am ]
Post subject:  Re: Status question : is this a bent four in the corner?
Robert. Are you saying that white Ko stone is dead by rule? Even if their aren't any dame?
Author:  RobertJasiek [ Tue Oct 30, 2012 5:54 am ]
Post subject:  Re: Status question : is this a bent four in the corner?
http://home.snafu.de/jasiek/difference_ ... rules.html

These headings of my commentary are relevant:
- Dead Stones in Sekis
- Perfect Pass
- Play out during the Alternation
- Clearly More Ko Threats

My first impression on applying these to a position incl. the particular shape: the KBA will have to adjudicate (if this occurs in a KBA tournament game) and presumably judge to score or continue the game, depending on available ko threats. I would, however, want to study for an hour or two to come to a definite conclusion on whether the KBA's arbitration is really needed.

Note that, simply speaking, Korean Rules depend also on ko threats while current Japanese Rules don't.
Author:  Bill Spight [ Tue Oct 30, 2012 9:02 am ]
Post subject:  Re: Status question : is this a bent four in the corner?
Magicwand wrote:
Robert. Are you saying that white Ko stone is dead by rule? Even if their aren't any dame?


Under the Japanese '89 rules the White ko stone is dead because Black can take and win the ko without giving rise to another uncapturable White stone. It is not removed because it is not within Black's territory.

The Japanese '89 rules are strange. ;)
Author:  RobertJasiek [ Tue Oct 30, 2012 9:45 am ]
Post subject:  Re: Status question : is this a bent four in the corner?
Magicwand wrote:
Are you saying that white Ko stone is dead by rule? Even if their aren't any dame?


After your edit, replacing Korean by Ko, let me answer also your now new question:

The ko stone is dead as a consequence of the rules' definitions and their application to that stone (as explained earlier). Dame are, according to the rules, identified after life and death have already been identified. If you have too much time, see also:

http://www.cs.cmu.edu/%7Ewjh/go/rules/Japanese.html
http://home.snafu.de/jasiek/j1989c.html
http://home.snafu.de/jasiek/j2003.html
http://home.snafu.de/jasiek/j2003inf.html
http://home.snafu.de/jasiek/j2003com.html
Author:  mitsun [ Tue Oct 30, 2012 9:58 am ]
Post subject:  Re: Status question : is this a bent four in the corner?
Bill Spight wrote:
Under the Japanese '89 rules the White ko stone is dead because Black can take and win the ko without giving rise to another uncapturable White stone. It is not removed because it is not within Black's territory.
The Japanese '89 rules are strange. ;)


Click Here To Show Diagram Code
[go]$$
$$ ------------------
$$ | W X X . O X .
$$ | . O . O O X .
$$ | O O O O X X .
$$ | X X X X X . .
$$ | . . . . . . .[/go]


If W does not intend to start and win the ko, then the marked move seems like a mistake. In an actual game, why would there be any scoring controversy? Instead of passing, B can capture the W stone and then fill the ko, gaining one point for the prisoner, which is removed from the board. Under area scoring rules, I suppose B also gets points for the dame he fills, and he can wait until there are no other dame on the board to get these points while W passes. Unless W has an inexhaustible supply of ko threats, W cannot prevent this outcome. Am I missing something?
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