Hi there,

The following position appeared in my last game.
I though my group was alive because it had 2 eyes, my opponent though it was seki... and the automatic score though it was dead.

What's the status of this white group?

Click Here To Show Diagram Code

[go]$$W
$$ ----------------
$$ - . . . . . . .
$$ - X X X . . . .
$$ - O O X . . . .
$$ - . O X X . . .
$$ - O O O X . . .
$$ - X X O X . . .
$$ - . X O X . . .
$$ - X . O X . . .
$$ - O O O X . . .
$$ - X X X X . . .
$$ - . . . . . . .[/go]

Show me the sequence to kill the inside black stones and I'll believe you that it isn't seki.

If you claim an area as white territory, you must be able to kill all black stones, which are located inside. Is this the case in your example?

White can't kill the stones because he'll be down to one liberty when he approaches. Black can't fill because he'll lose a liberty as well.

Therefor: seki.

Click Here To Show Diagram Code

[go]$$W
$$ ----------------
$$ - . . . . . . .
$$ - X X X . . . .
$$ - O O X . . . .
$$ - . O . X . . .
$$ - O O O X . . .
$$ - X X O X . . .
$$ - . X O X . . .
$$ - X 1 O X . . .
$$ - O O O X . . .
$$ - X X X X . . .
$$ - . . . . . . .[/go]

You should have given atari at Black's four stones, latest before the very last outside liberty of your own group disappeared.

Click Here To Show Diagram Code

[go]$$W
$$ ----------------
$$ - . . . . . . .
$$ - X X X . . . .
$$ - O O X . . . .
$$ - . O 2 X . . .
$$ - O O O X . . .
$$ - X X O X . . .
$$ - 3 X O X . . .
$$ - X O O X . . .
$$ - O O O X . . .
$$ - X X X X . . .
$$ - . . . . . . .[/go]

You willh have to take Black's stones off the board.

Click Here To Show Diagram Code

[go]$$W
$$ ----------------
$$ - . . . . . . .
$$ - X X X . . . .
$$ - O O X . . . .
$$ - . O X X . . .
$$ - O O O X . . .
$$ - . . O X . . .
$$ - O . O X . . .
$$ - . O O X . . .
$$ - O O O X . . .
$$ - X X X X . . .
$$ - . . . . . . .[/go]

Now you have three eyes, five points of territory, and four prisoners.

_________________
The really most difficult Go problem ever: https://igohatsuyoron120.de/index.htm
Igo Hatsuyōron #120 (really solved by KataGo)

However possibly misunderstanding something.

A group in seki isn't dead, it is alive in seki. You two weren't in diagreement. If there is a seki situation, there will always be two eyes.

Here both the white group and the black group are alive in seki.

Looks like I'm so used with the "two-eyes" white is alive.. that I forgot that it doesn't mean the black stones inside are dead.
Actually, I never though about this possibility.. for some reason I assumed that any group without eyes inside my "2-eyed" group were dead.
Now, thinking about it, I'm glad this situation happened in my game.

I don't understand this statement. The first example on Sensei's Library seems to show the opposite.

http://senseis.xmp.net/?Seki

Indeed, it happened to me too. I had two completely separated eyes, so I was alive.
I was playing against the software Many Faces of Go. I was used to see it throw stones uselessly, so I didn't bother, until I told myself "hey, this group is running out of liberties, time to capture the dead stones... WTF ?!?"

The possibility to make such a seki with three stones around a corner is common :