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 Post subject: Cho Chikun's problem nr. 372 - black can be cut
Post #1 Posted: Mon Mar 22, 2021 9:22 am 
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The following is a problem of Cho Chikun's Life & Death Elementary problems nr. 372.

Click Here To Show Diagram Code
[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?

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 Post subject: Re: Cho Chikun's problem nr. 372 - black can be cut
Post #2 Posted: Mon Mar 22, 2021 5:37 pm 
Honinbo

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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:

Click Here To Show Diagram Code
[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]

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 Post subject: Re: Cho Chikun's problem nr. 372 - black can be cut
Post #3 Posted: Tue Mar 23, 2021 6:00 am 
Gosei
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It's a good question and it leads to a higher level argument:

Click Here To Show Diagram Code
[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 :b1: reducing the eyespace to a bulky five and then :b3: 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.

Click Here To Show Diagram Code
[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.

Click Here To Show Diagram Code
[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.

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 Post subject: Re: Cho Chikun's problem nr. 372 - black can be cut
Post #4 Posted: Tue Mar 23, 2021 7:49 am 
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Kirby wrote:
Click Here To Show Diagram Code
[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]
To me this sequence seems quite dangerous. The only answer seems to be J18 which is quite unfavorable for black.

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 Post subject: Re: Cho Chikun's problem nr. 372 - black can be cut
Post #5 Posted: Tue Mar 23, 2021 7:55 am 
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Knotwilg wrote:
The common technique for capturing is :b1: reducing the eyespace to a bulky five and then :b3: 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.
I think the answer to this problem is supposed to be for black to play B18 first.

Click Here To Show Diagram Code
[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]

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 Post subject: Re: Cho Chikun's problem nr. 372 - black can be cut
Post #6 Posted: Tue Mar 23, 2021 10:56 am 
Honinbo

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mkdrive2 wrote:
Kirby wrote:
Click Here To Show Diagram Code
[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]
To me this sequence seems quite dangerous. The only answer seems to be J18 which is quite unfavorable for black.


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.

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 Post subject: Re: Cho Chikun's problem nr. 372 - black can be cut
Post #7 Posted: Tue Mar 23, 2021 3:20 pm 
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Kirby wrote:
My thought is that black can crawl to get liberties, and white won't have enough liberties (if black plays to kill first).
You are right. Black can just capture the white stones before running out of liberties. I guess that answers my question.
Click Here To Show Diagram Code
[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]

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