The following is a problem of Cho Chikun's Life & Death Elementary problems nr. 372.

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[go]$$Bc
$$--------------
$$| . . . . O . . . .
$$| . . . O X . X . .
$$| O O O O . X . . .
$$| X X X X X . . . .
$$| X O O . . . . . .
$$| . . . . . . . . .
$$| . O . . . . . . .[/go]

I wanted to ask if I am right that black has a vulnerability here where he can be cut, namely F16. In this situation is it really the right move to kill white?

It's a good thing to be concerned about. I don't really feel that it's that dangerous, though.

I guess it could be interesting to think about what happens here:

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[go]$$Wc
$$--------------
$$| . . . . O . . . .
$$| . . . O X 2 X . .
$$| O O O O 1 X . 7 .
$$| X X X X X 3 . . .
$$| X O O . . 5 . . .
$$| . . . 6 4 . . . .
$$| . O . . . . . . .[/go]

_________________
be immersed

It's a good question and it leads to a higher level argument:

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[go]$$Bc
$$--------------
$$| . . 2 1 O . . . .
$$| . 3 . O X 5 X . .
$$| O O O O 4 X . . .
$$| X X X X X 6 . . .
$$| X O O . . . . . .
$$| . . . . . . . . .
$$| . O . . . . . . .[/go]

The common technique for capturing is reducing the eyespace to a bulky five and then strike at the vital point. In Black's favor, the usual 8-1=7 internal liberties are now 3 because of the special properties of the corner. In White's favor there's a ko at the outside.

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[go]$$Bc
$$--------------
$$| . . 1 2 O . . . .
$$| 7 3 . O X 5 X . .
$$| O O O O 4 X . . .
$$| X X X X X 6 . . .
$$| X O O . . . . . .
$$| . . . . . . . . .
$$| . O . . . . . . .[/go]

So Black may capture with less aji in this fashion.

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[go]$$Bc
$$--------------
$$| . 2 1 . O . . . .
$$| 4 3 . O X 5 X . .
$$| O O O O 4 X . . .
$$| X X X X X 6 . . .
$$| X O O . . . . . .
$$| . . . . . . . . .
$$| . O . . . . . . .[/go]

But this is deceptive: White can make a ko.

To me this sequence seems quite dangerous. The only answer seems to be J18 which is quite unfavorable for black.

I think the answer to this problem is supposed to be for black to play B18 first.

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

My thought is that black can crawl to get liberties, and white won't have enough liberties (if black plays to kill first).


Globally, it could turn out not bad for white, though.

_________________
be immersed

You are right. Black can just capture the white stones before running out of liberties. I guess that answers my question.

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[go]$$Wcm2
$$--------------
$$| . . . . O . . . .
$$| 8 X 0 O X 2 X 9 .
$$| O O O O 1 X . 7 .
$$| X X X X X 3 . . .
$$| X O O . . 5 . . .
$$| . . . 6 4 . . . .
$$| . O . . . . . . .[/go]