I'm reading "The breakthrough to Shodan". Not that I have any hopes.
I'm not sure about the first problem in Ch 9.

Click Here To Show Diagram Code

[go]$$c
$$ | . . . , . . . . . , .
$$ | . . . . . . . . . . .
$$ | . X X . . . . . . . .
$$ | . O X . . . . . . . .
$$ | . O O X . . . . . . .
$$ | . . O X . . . . . . .
$$ | . O X X . O . . . X .
$$ | . . O . X O . . . . .
$$ | . . . . X . . . . . .
$$ | . . . . . . . . . . .
$$ +-----------------------[/go]

The question is: what is B's best endgame move.

The wrong answer is here:


The right answer is:


My guess:


correct?

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I think I am so I think I am.

White will connect with at , thereafter capture the Ko in the corner first.

But because this is an endgame problem, Ko is no option for White anyway.

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

What about at ?

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Main Entry: zing·er Pronunciation: \ˈziŋ-ər\
1 : something causing or meant to cause interest, surprise, or shock
2 : a pointed witty remark or retort

Ends in Ko also.

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

It took me some time to digest. But here is what I learnt:
The solutions of the book, of Cassandra and of zinger all leads to ko with Black capturing first. They are all three ( equally) good refutations for W's blocking move @2. W shouldn't risk ko for some yosepoints.

book's refutation:


Cassandra:


Zinger:

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I think I am so I think I am.

One of these things is not like the other...

True enough. But what I meant was:

Click Here To Show Diagram Code

[go]$$c
$$ | . . . . . . .
$$ | . X X . . . .
$$ | . O X . . . .
$$ | . O O X . . .
$$ | . . O X . . .
$$ | 5 O X X . O .
$$ | . 3 O . X O .
$$ | 4 1 2 . X . .
$$ | . . . . . . .
$$ +---------------[/go]

_________________
Main Entry: zing·er Pronunciation: \ˈziŋ-ər\
1 : something causing or meant to cause interest, surprise, or shock
2 : a pointed witty remark or retort

That's why I put your name in quotes instead of just saying "Zinger's diagram." He had it labeled as yours but it wasn't.

He (cyclops) apologizes for misusing Zingers name. Don't know how he got so confused.
But then his (Z's) true move (B5 ) is suboptimal because W gets to make the first ko capture.
( W7@8 -> B8@10 : threatens fatal atari next @7 or above 5)
Or maybe cyclops is myopic beyond repair?

BTW, the initial position is discussed also in "Basic Techniques of Go" by Haruyama & Nagahara ( Ch 5, dia 43, p 101 ).

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I think I am so I think I am.

Haha, sorry - ethanb has a hard time judging what's polite in terms of pronouns in a forum like this. Better to use names.

But 9 can be a hane on the outside, then white will have to throw in to start the ko (so black captures first anyway, as well as making it a direct ko rather than approach-move.)

Click Here To Show Diagram Code

[go]$$cW4@a
$$ | . . . . . . .
$$ | . X X . . . .
$$ | . O X . . . .
$$ | . O O X . . .
$$ | . 6 O X . . .
$$ | 5 O X X . O .
$$ | 7 3 O . X O .
$$ | 4 1 2 . X . .
$$ | . 8 . . . . .
$$ +---------------[/go]

No need to say sorry; Cyclops was not offended. I am confused about your last remark. W8 is an atari and B has no choice but to play in the very corner. Or do we talk different diagrams?

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I think I am so I think I am.

We talk late in the evening, I think - I forgot that a marked a stone earlier.