9-point corner shape confusion

[jdl]

This came up in a game I'm playing. I already made my move, so you aren't spoiling anything. As white, I was worried that black could cause trouble (such as a ko) by playing at A. I played S1 just to be extra safe, since I'm ahead by a lot. If it was a close game though, I would hate to give away a free point.

Can black do anything interesting here, or am I paranoid?

[leichtloeslich]

Can black do anything interesting here?

I dont think so, since white has a guaranteed eye.

[jdl]

White S1 in response to black A?

If that's right then I think I see where I was going wrong in my reading. I kept ending up with a black ko in my head, but I don't think it's actually there.

[leichtloeslich]

White S1 in response to black A?

If you do that then I think black s3 can get a ko or seki.
I would just simply make an eye, so black A - white s3. After that I dont see anything for black.

[jdl]

Ok, thanks.

This is what I was seeing in my head, thinking it was a ko, but it really isn't because of the double-atari.

[Bill Spight]

Never mind.

[yoyoma]

Ok, thanks.

This is what I was seeing in my head, thinking it was a ko, but it really isn't because of the double-atari.

I think is a mistake, Black can take the ko, and next extend upwards from (so a two step ko). Instead white should make an eye on the top side. Now if black starts a ko on the bottom, white is alive in double ko.

[jdl]

I think is a mistake, Black can take the ko

I'm not seeing the ko that you're referring to. B5 isn't on the board yet.

[yoyoma]

I think is a mistake, Black can take the ko

I'm not seeing the ko that you're referring to. B5 isn't on the board yet.

Wow I hallucinated that one!

[Alexfrog]

I think is a mistake, Black can take the ko

I'm not seeing the ko that you're referring to. B5 isn't on the board yet.

Wow I hallucinated that one!

Hehe, we've all done that sometimes.

In this the original 9 point sarea in this thread is safe, but if itwere one smaller, a rectangular eight, without the space at R1, then you would indeed need to play inside. Otherwise your opponent could invade and get either a seki or ko depending on how you responded.

[leichtloeslich]

I hallucinated that one

you're obviously not alone. I often looked at this corner and thought "uhm, doesnt black have to defend?"

$$B
$$ +------------
$$ | . . . X O .
$$ | . X . X O .
$$ | . . X X O .
$$ | X X O O O .
$$ | O O O . . .
$$ | . . . . . .

Click Here To Show Diagram Code

[go]$$B
$$ +------------
$$ | . . . X O .
$$ | . X . X O .
$$ | . . X X O .
$$ | X X O O O .
$$ | O O O . . .
$$ | . . . . . .[/go]

I guess these are shapes where our seki/ko pattern recogition misfires because there's a forcing move inside and we can make that corner ko shape aroung the 1-1 point, but even with the forcing move the attacker cant get an eye while the defender already has one, therefore no seki or ko anywhere in this thread.