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Offline Ian Butler
 Post subject: A corner L&D
Post #1 Posted: Thu Dec 20, 2018 11:33 am 
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A fun corner L&D I came across in a game by Yuan Zhou.

White makes an endgame mistake after the exchange white A, black B. (triangled stone is there only to illustrate black is strong there and can't be cut. There was no actual stone on that position, but it matters not in this L&D)
White plays tenuki.
Black to kill.

Image

Answer:
Image


Explanation:
After the exchange of A and B, white needs to add another move in the corner. If he doesn't, black kills by cutting. White can atari the stone but is then stuck in a liberty problem. He cannot atari the stones once white drops down (either way) and is dead in the corner, making for a 30 point swing in the game.

The mistake, says Yuan Zhou, lays earlier in the cirkled stone move. He played that one instead of 2, making black's 1 sente that has to be answered at white 2 instead of at the squared spot. Hope this makes sense because I saw the game and maybe it's not clear from only this position. 1 and 2 weren't played yet and white played the cirkled stone instead of 2, that's what I mean.

The second mistake was playing tenuki, of course.
Image

This post by Ian Butler was liked by 2 people: Leon, MikeKyle
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Offline Leon
 Post subject: Re: A corner L&D
Post #2 Posted: Sun Dec 23, 2018 3:00 am 
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This is both a fun and an instructive problem (I think that positions like this are sometimes referred to as the Golden Chicken Standing on One Leg https://senseis.xmp.net/?GoldenChickenStandingOnOneLeg).

Here is a related but yet very different position: Don't let the golden chicken ruin your christmas and survive as black:

Click Here To Show Diagram Code
[go]$$c Black to live. (Edit: I fixed a mistake in the original problem. Thank you Shaddy.)
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . X O . . . . |
$$ | . . . . . . . . . . . O O X O X X O . |
$$ | . . . . . . . . . . . . . X X O O X . |
$$ | . . . , . . . . . , . . O . O , O X . |
$$ | . . . . . . . . . . . . O . O . O O . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . O . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]


Last edited by Leon on Tue Dec 25, 2018 2:27 am, edited 2 times in total.
This post by Leon was liked by 3 people: ez4u, macelee, MikeKyle
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Offline MikeKyle
 Post subject: Re: A corner L&D
Post #3 Posted: Sun Dec 23, 2018 4:48 pm 
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KGS: MKyle
Thanks both. The first post is a really nice example of a sensible enough looking but deadly endgame blunder.

The second post has three of my favourite things:
- Poetry
Leon wrote:
Don't let the golden chicken ruin your christmas


- A really fun novel problem that is achievable but not obvious at my level

And..
- Under the stones magic
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Offline Shaddy
 Post subject: Re: A corner L&D
Post #4 Posted: Mon Dec 24, 2018 6:39 pm 
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KGS: Str1fe, Midorisuke
Click Here To Show Diagram Code
[go]$$c Black to live.
$$ ---------------------------------------
$$ | . . . . . . . . . . . . 4 X 6 5 . 2 . |
$$ | . . . . . . . . . . . . O X O X X O 1 |
$$ | . . . . . . . . . . . . O X X O O X 3 |
$$ | . . . , . . . . . , . . O . O , O X . |
$$ | . . . . . . . . . . . . O . O . O O . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . O . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

This post by Shaddy was liked by 3 people: Bill Spight, ez4u, Leon
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Offline mhlepore
 Post subject: Re: A corner L&D
Post #5 Posted: Mon Dec 24, 2018 7:32 pm 
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Yuan Zhou wrote a book (which I'm not sure if it's in print anymore), where reviews a game that he lost because of this life and death problem. He was ahead, thought his corner was alive, so he tenukied.

So it can be a blind spot for even strong players.
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Offline Leon
 Post subject: Re: A corner L&D
Post #6 Posted: Tue Dec 25, 2018 2:24 am 
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Rank: EGF 2d
Shaddy wrote:
Click Here To Show Diagram Code
[go]$$c Black to live.
$$ ---------------------------------------
$$ | . . . . . . . . . . . . 4 X 6 5 . 2 . |
$$ | . . . . . . . . . . . . O X O X X O 1 |
$$ | . . . . . . . . . . . . O X X O O X 3 |
$$ | . . . , . . . . . , . . O . O , O X . |
$$ | . . . . . . . . . . . . O . O . O O . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . O . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

Oof, how embarassing for me. I will fix the problem. Thank you
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