Seki with eyes question 6

Yet another interesting seki with eyes:

Outer stones alive (2)  

This is a seki too, even though White can capture the two Black stones in the corner (but does not benefit from doing so!).

-- jvt

Why would this be a seki? White plays the 2-2 point, and can then play the 1-1 point to make 2 eyes. Something must be missing here.

-- bp

Using Chinese rules:
Black: 1 point, White: 2 points.

Using Japanese rules:
Black: 0 points, White: 0 points.

Outer stones alive (2)  

If White plays , Black will throw in with . White can only capture the two stones with and allow Black to capture two stones with .

Using Chinese rules:
Black: 4 points, White: 4 points.

Using Japanese rules:
Black: 2 points, White: 2 points.

Using either ruleset, White does not gain by playing at the 2-2 point.

--unkx80

I disagree with the chinese rules points total. White loses a point under chinese scoring by playing 1 (count the stones and the empty points). Both sides claim 2 prisoners, but the place where white played 1 didn't count towards black's territory in the first place (unlike 2 and 4). The chinese counts for the 2 diagrams should be

Using Chinese rules:
Black: 3 points, White: 10 points.

Using Chinese rules:
Black: 4 points, White: 10 points.

Bill: Under Japanese '89 rules, if this position remains at the end of the game, Black's two stones are considered to be alive, even though White to play can capture them. The following is not real play, which has ended. Rather it is a demonstration.

Gone but not dead  

After the play is over, White claims that the stones are dead. And indeed, she can capture them with - . However:

jvt: This is taken straight out of Life-and-Death example 2 in the Japanese Rules 1989.
The two Black stones are alive: if White captures Black's two stones, Black can play two new stones (at and ) which White cannot capture. Since there is a dame, the position is a seki.

Bill: Jean-Pierre's point, which had originally slipped my mind, is that the capture of the stones allows new living stones ( and ) to be played. Therefore, at the end of play, the stones are considered to be alive.
It sounds peculiar, but the Japanese '89 rules for post-play demonstrations provide a logical basis for most of the special rulings of the Japanese '49 rules.

jwaytogo: It should be noted that playing at the 2-2 point does not always result in a loss of points, and one should look at the specific situation and the specific ruleset. Below are some examples of similar situations. Sometimes, playing at the 2-2 results in a loss for white, sometimes in a gain. Can you figure out what happens in each of the following? (Hint: think under the stones)

If white stands to gain by playing at the 2-2 point, this also means there is value to black sacrificing a stone to ensure the seki remains.

Example 1  

Example 2  

Example 3  

Example 4  

Example 5  

Isildur: jwaytogo, perhaps I'm missing something, but I don't see that white has anthing to gain by playing the 2-2 in any of these examples. In all of these cases, white stands to lose even more upper stones (and the potential territory beneath them) than the two in the initial example on this page, thus making playing the 2-2 atari bad for white in all of these cases. It seems to me that black doesn't need to actively do anything to keep any of these five cases as sekis, because it's not in white's interest to break any of the sekis in the first place.

LukeNine45: If white can recapture with an under-the-stones tesuji, then white might gain points, depending on how many stones white loses. E.g.:

Example 1.5  

Example 1.5  

Example 1.5  

White has 4 points here now vs. 1 before playing . I don't think this position (where white has the under-the-stones option) should be called a seki.

Isildur: Ah, I didn't think of that, thanks. I guess I should have thought that through a bit more. =P

Paul: I don't understand why this is a Seki.

What if White plays here:

White wins the corner?  

White has two eyes, and the two black stones in the corner are dead.

Bill: White has one eye, Black has one eye, and they share one liberty. It's a seki.

After , if the Black stones are dead, how does White capture them? If White approaches them, Black will capture the White stones instead.

Paul: Thank you for the explanation. I am still new to the game, and didn't see that White could not capture the two Black stones. White can only capture the two Black stones while White has the two other liberties to keep the White stones alive. By making an eye, White loses a liberty and any attempt to take the Black stones will put White in atari, allowing Black to capture the White stones.