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 Post subject: Lee Changho tesuji book 1 problem 92
Post #1 Posted: Sun Oct 13, 2019 4:46 am 
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One of these problems is not like the others...

Book 1 of the LCH tesjui set is mostly "spot the key point" capturing races, where the continuation is a one-way street. But problem 92 seems to have a lot more variations than anything else in the book. As far as I can tell, there are actually two ways for black to capture the white stones on the left. Does anyone else agree?

Click Here To Show Diagram Code
[go]$$c Black to play.
$$ | . . . , . . . . . ,
$$ | . . . . . . . . . .
$$ | . . X . . . . . . .
$$ | . X . . . . . . . .
$$ | . O X . . . . . . .
$$ | . O X . X . . . . .
$$ | . O O X . . . . . ,
$$ | O X X O O O . . . .
$$ | . . . . . . . . . .
$$ | . . . . . . . . . .
$$ ---------------------[/go]

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 Post subject: Re: Lee Changho tesuji book 1 problem 92
Post #2 Posted: Sun Oct 13, 2019 10:20 am 
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The first thing that appear to work that I see is this :

Click Here To Show Diagram Code
[go]$$c Black to play.
$$ | . . . , . . . . . ,
$$ | . . . . . . . . . .
$$ | . . X . . . . . . .
$$ | 5 X . . . . . . . .
$$ | . O X . . . . . . .
$$ | 2 O X . X . . . . .
$$ | . O O X . . . . . ,
$$ | O X X O O O . . . .
$$ | 1 a 3 . . . . . . .
$$ | . 4 . . . . . . . .
$$ ---------------------[/go]


Black only has two liberties and can't really increase them so an atari is the first thing to look at.

:b2: at "a" obviously fail because it's the corner, so trying for a ko seems to be white's strongest resistance. :b3: increase liberties and threaten to live in the corner which would capture the six white stones, so :w4: is forced then :b5: win the capturing race


Next some other moves that might be worth exploring but fail :

Click Here To Show Diagram Code
[go]$$c Black to play.
$$ | . . . , . . . . . ,
$$ | . . . . . . . . . .
$$ | . . X . . . . . . .
$$ | 7 X . . . . . . . .
$$ | . O X . . . . . . .
$$ | 6 O X . X . . . . .
$$ | 5 O O X . . . . . ,
$$ | O X X O O O . . . .
$$ | 4 2 1 8 . . . . . .
$$ | . 3 . . . . . . . .
$$ ---------------------[/go]


Click Here To Show Diagram Code
[go]$$c Black to play.
$$ | . . . , . . . . . ,
$$ | . . . . . . . . . .
$$ | . . X . . . . . . .
$$ | . X . . . . . . . .
$$ | . O X . . . . . . .
$$ | . O X . X . . . . .
$$ | . O O X . . . . . ,
$$ | O X X O O O . . . .
$$ | . 2 3 4 . . . . . .
$$ | . . 1 . . . . . . .
$$ ---------------------[/go]



Click Here To Show Diagram Code
[go]$$c Black to play.
$$ | . . . , . . . . . ,
$$ | . . . . . . . . . .
$$ | . . X . . . . . . .
$$ | . X . . . . . . . .
$$ | . O X . . . . . . .
$$ | . O X . X . . . . .
$$ | . O O X . . . . . ,
$$ | O X X O O O . . . .
$$ | 6 2 3 1 4 . . . . .
$$ | . 5 . . . . . . . .
$$ ---------------------[/go]


And there's this one which I thought failed but might actually not :

Click Here To Show Diagram Code
[go]$$c Black to play.
$$ | . . . , . . . . . ,
$$ | . . . . . . . . . .
$$ | . . X . . . . . . .
$$ | . X . . . . . . . .
$$ | . O X . . . . . . .
$$ | . O X . X . . . . .
$$ | . O O X . . . . . ,
$$ | O X X O O O . . . .
$$ | 2 1 . . . . . . . .
$$ | . 3 . . . . . . . .
$$ ---------------------[/go]

:b3: gains a liberty so black win

Click Here To Show Diagram Code
[go]$$c Black to play.
$$ | . . . , . . . . . ,
$$ | . . . . . . . . . .
$$ | . . X . . . . . . .
$$ | 7 X . . . . . . . .
$$ | . O X . . . . . . .
$$ | 4 O X . X . . . . .
$$ | . O O X . . . . . ,
$$ | O X X O O O . . . .
$$ | 3 1 . 5 6 . . . . .
$$ | . 2 . . . . . . . .
$$ ---------------------[/go]

Being clver and trying to set up a ko ultimately fail

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 Post subject: Re: Lee Changho tesuji book 1 problem 92
Post #3 Posted: Sun Oct 13, 2019 3:56 pm 
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Thanks bki, looks good to me. Your very first diagram is the variation diagram from the book (white has a less tricky but more profitable response which is given as the main line). All your failure variations are not in the book, and I agree that they fail. Your very last diagram is given in the book as failure, but I agree with you that it succeeds.

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 Post subject: Re: Lee Changho tesuji book 1 problem 92
Post #4 Posted: Mon Oct 14, 2019 3:52 am 
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By the way, the tesuji-looking :w4: in the following is why I thought this second variation failed initially :

Click Here To Show Diagram Code
[go]$$c Black to play.
$$ | . . . , . . . . . ,
$$ | . . . . . . . . . .
$$ | . . X . . . . . . .
$$ | . X . . . . . . . .
$$ | . O X . . . . . . .
$$ | . O X . X . . . . .
$$ | . O O X . . . . . ,
$$ | O X X O O O . . . .
$$ | 2 1 . 5 . . . . . .
$$ | . 3 4 . . . . . . .
$$ ---------------------[/go]


But after :b5:, black make an eye and white can't ever capture black. :w4: at C2 also obviously fail for the same reason, and anything else fail by simply counting liberties.

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 Post subject: Re: Lee Changho tesuji book 1 problem 92
Post #5 Posted: Mon Oct 14, 2019 4:17 am 
Oza
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This is what I saw:

Click Here To Show Diagram Code
[go]$$c Black to play.
$$ | . . . , . . . . . ,
$$ | . . . . . . . . . .
$$ | . . X . . . . . . .
$$ | 9 X . . . . . . . .
$$ | . O X . . . . . . .
$$ | 2 O X . X . . . . .
$$ | . O O X . . . . . ,
$$ | O X X O O O . . . .
$$ | 1 3 . 5 8 . . . . .
$$ | . 4 6 7 . . . . . .
$$ ---------------------[/go]


Either I have a blind spot, or this line is rejected as White get too many free points

Click Here To Show Diagram Code
[go]$$c Black to play.
$$ | . . . , . . . . . ,
$$ | . . . . . . . . . .
$$ | . . X . . . . . . .
$$ | . X . . . . . . . .
$$ | . O X . . . . . . .
$$ | . O X . X . . . . .
$$ | 3 O O X . . . . . ,
$$ | O X X O O O . . . .
$$ | 1 2 4 . . . . . . .
$$ | . . . . . . . . . .
$$ ---------------------[/go]


This is probably the main line: White forces a capture in sente

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 Post subject: Re: Lee Changho tesuji book 1 problem 92
Post #6 Posted: Mon Oct 14, 2019 5:31 am 
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Yep, your second diagram is the first answer diagram in the book. I guess it's easier to read out, even if it does let white have a bigger corner.

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 Post subject: Re: Lee Changho tesuji book 1 problem 92
Post #7 Posted: Mon Oct 14, 2019 10:18 am 
Gosei
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Interesting, that the hane-variation was considered first by so many. My eyes immediately went to make the guzumi : D

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