Big dan didn't see it

[Knotwilg]

Yesterday I was watching an IGS game. Jirohachi 7d was playing White giving 3 handicap stones. He had just lost a ko and executed on his ko threat to kill a big group. He only caught a small part of it and the big tail was alive.

At move 133 a spectator started asking about J11, as this would kill the group according to him. Obviously this was not true, since Black could make two eyes at the right side. I wasn't logged in so I could not reply. But then I saw it ... The comments kept coming in but nobody saw it. Even Jirohachi 7d did not see it. I checked it a few times to be sure. I felt like that lone spectator knowing who is the bad guy. "There there, behind you!"

Go to 133. Do you see it?

[Loons]

133 s7 starts a ko? Oh, except it doesn't.

[Knotwilg]

So, S7 - J11. What's next?

[Uberdude]

then t10 and ko

[HermanHiddema]

@Uberdude: Then S8 and there's nothing?

@Knotwilg: You're looking at S5, presumably? Then after L11, T10 makes ko?

So then first black exchanges T10 for white T11, then makes an eye with black L11, white S7, black T6 and black lives?

[Knotwilg]

I'm with Uberdude.
White S5
Black L11 (sorry for the J11 confusion earlier)
White T10
Herman, if Black S8, then T6 is ko.

Edit: in your variation, White will not S7 but capture at T9.

[HermanHiddema]

@knotwilg: Uberdude is following up on S7-L11. Then after T10-S8 you can't play T6, it is suicide.

In my variation, capturing at T9 doesn't help, black captures at R10 and the double ko works to black's advantage.

[Uberdude]

Oh I didn't actually read Loon's coordinate, I assumed he said s5 first as s7 never occurred to me: is it ever a good move in such a shape?.
And yeah t10 t11 exchange (w does need to answer because of s13 weakness) means black lives in double ko, but it would be dead in ko if white just connected at r10 instead of r11 (or is there then some problem around r12?).

[Knotwilg]

Herman, there is no double ko for me. Here's my variation:
S5-T10-T11-L11-T9-R10-S7

Of course at almost any step Black can resolve the ko.

[HermanHiddema]

@knotwilg: After S7, black can take at T11. Then it is not double ko, because White can play that ko, but black can resolve the ko with S11, after which R12 captures some stones, so the ko is then not without risk for white either, and black takes first.

[Knotwilg]

Then we agree: it's not a picknick ko for White but I'm not sure both players knew all that and just left it as aji.

[Bill Spight]

I tell you, reading this discussion makes me think that maybe Ed Lee is right. No coordinates, please.

There are ko positions here like I have never seen before. Very interesting.

It is hard for me to think that Jirohachi did not see the ko, given the play leading up to :w133:. But I think that he saw that it was an approach ko with Black to take first, and thought (erroneously, IMO) that taking some stones in sente was best.



Edited some variations.

Edit: I am not at all sure about the W O-10, B N-09 exchanges. This is an unusual ko situation, which I will be studying some more.

[mitsun]

So we should call this is an approach-ko ko, rather than an approach-move ko?
(W must win the first ko in order to earn the opportunity to start the killing ko.)