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Offline ez4u
 Post subject: Re: Recent 9x9 game
Post #21 Posted: Mon Sep 19, 2011 2:30 am 
Oza
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jts wrote:
Click Here To Show Diagram Code
[go]$$W
$$ +-------------------+
$$ | . . . . . . c b . |
$$ | . . 2 X O a 0 9 d |
$$ | X X 1 6 X 5 7 X . |
$$ | X O X X 4 3 X . 8 |
$$ | O O X O X X O X X |
$$ | . O O O W X O O O |
$$ | . . . . O O . . . |
$$ | . . . . . . . . . |
$$ | . . . . . . . . . |
$$ +-------------------+[/go]
Or :w13: descends and the ko is on the other side. But this is an unwinnable double ko for B, right? Is there a better one?

In this case there is nothing. After :b8:, White captures with :w9: and Black has no ko threat.
Click Here To Show Diagram Code
[go]$$Wc
$$ +-------------------+
$$ | . . . . . . . . . |
$$ | . . 2 X O . . . . |
$$ | X X 1 6 X 5 7 X . |
$$ | X O X X 4 3 X 9 8 |
$$ | O O X O X X O X X |
$$ | . O O O W X O O O |
$$ | . . . . O O . . . |
$$ | . . . . . . . . . |
$$ | . . . . . . . . . |
$$ +-------------------+[/go]

Herman's ko should be this
Click Here To Show Diagram Code
[go]$$Wc
$$ +-------------------+
$$ | . . . . . . . . . |
$$ | . . 2 X O . 0 9 . |
$$ | X X 1 6 X 5 7 X . |
$$ | X O X X 4 3 X 8 . |
$$ | O O X O X X O X X |
$$ | . O O O W X O O O |
$$ | . . . . O O . . . |
$$ | . . . . . . . . . |
$$ | . . . . . . . . . |
$$ +-------------------+[/go]

However, after :w15:, Black has no ko threats. So correct play from the original position is for Black to exchange "a" for "b" to create a ko threat and then pass!? :scratch:
Click Here To Show Diagram Code
[go]$$Wcm11
$$ +-------------------+
$$ | . . . . . . 3 2 5 |
$$ | . . X X O 1 X O 4 |
$$ | X X . X X O O X . |
$$ | X O X X X O X X . |
$$ | O O X O X X O X X |
$$ | . O O O O X O O O |
$$ | . . . . O O a b . |
$$ | . . . . . . . . . |
$$ | . . . . . . . . . |
$$ +-------------------+[/go]

However! In this case White also has two ko threats starting with :w5: so White will end up winning the ko. Sheesh! See any errors here?
Click Here To Show Diagram Code
[go]$$Wc
$$ +-------------------+
$$ | . . . . . . O 4 1 |
$$ | . 5 X X O O . O X |
$$ | X X . X X O O X . |
$$ | X O X X X O X X . |
$$ | O O X O X X O X X |
$$ | . O O O O X O O O |
$$ | . . . . O O X O . |
$$ | . . . . . . 3 2 . |
$$ | . . . . . . . . . |
$$ +-------------------+[/go]

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Last edited by ez4u on Mon Sep 19, 2011 3:56 am, edited 1 time in total.
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Offline ez4u
 Post subject: Re: Recent 9x9 game
Post #22 Posted: Mon Sep 19, 2011 4:07 am 
Oza
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Helel wrote:
ez4u wrote:
However! In this case White also has two ko threats starting with :w5: so White will end up winning the ko. Sheesh! See any errors here?

Since my reading is pretty awful I'm in all likelihood imagining things, but what I had thought was that one of white's ko threats disappeared if black played b8 instead of c8...

Great idea! So that leaves us with the position below and White has no other ko threat after :b10: recaptures the ko. Black does not have to add a stone in the original position. :rambo:

Oops! Still wrong. At this point White connects at "a". When Black plays "b", White recaptures the ko and Black has no threats left. White has no internal connection that helps the situation. :o
Click Here To Show Diagram Code
[go]$$Wc :w7:, :b10: take ko
$$ +-------------------+
$$ | . . . 5 b . O 4 1 |
$$ | . X 6 X O O a O X |
$$ | X X O X X O O X . |
$$ | X O X X X O X X . |
$$ | O O X O X X O X X |
$$ | . O O O O X O O O |
$$ | . . . . O O X O 8 |
$$ | . . . . . . 3 2 9 |
$$ | . . . . . . . . . |
$$ +-------------------+[/go]

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"Short-lived are both the praiser and the praised, and rememberer and the remembered..."
- Marcus Aurelius; Meditations, VIII 21
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Offline gaius
 Post subject: Re: Recent 9x9 game
Post #23 Posted: Mon Sep 19, 2011 4:58 am 
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@ez4u:
In your first diagramme, you can swap the order of :w7: and :w9:. Then black cannot avoid the hopeless ko (except of course, if he sacrifices two stones, but that also loses the game :)).
Click Here To Show Diagram Code
[go]$$Wc
$$ +-------------------+
$$ | . . . . . . . . . |
$$ | . . 2 X O . . . . |
$$ | X X 1 6 X 5 9 X . |
$$ | X O X X 4 3 X 7 8 |
$$ | O O X O X X O X X |
$$ | . O O O W X O O O |
$$ | . . . . O O . . . |
$$ | . . . . . . . . . |
$$ | . . . . . . . . . |
$$ +-------------------+[/go]

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This post by gaius was liked by: ez4u
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Offline ez4u
 Post subject: Re: Recent 9x9 game
Post #24 Posted: Mon Sep 19, 2011 5:39 am 
Oza
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gaius wrote:
@ez4u:
In your first diagramme, you can swap the order of :w7: and :w9:. Then black cannot avoid the hopeless ko (except of course, if he sacrifices two stones, but that also loses the game :)).
Click Here To Show Diagram Code
[go]$$Wc
$$ +-------------------+
$$ | . . . . . . . . . |
$$ | . . 2 X O . . . . |
$$ | X X 1 6 X 5 9 X . |
$$ | X O X X 4 3 X 7 8 |
$$ | O O X O X X O X X |
$$ | . O O O W X O O O |
$$ | . . . . O O . . . |
$$ | . . . . . . . . . |
$$ | . . . . . . . . . |
$$ +-------------------+[/go]

Yes!!! So finally there is not even a glorious defeat, and Black has nothing to do but submit. :-|

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"Short-lived are both the praiser and the praised, and rememberer and the remembered..."
- Marcus Aurelius; Meditations, VIII 21
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Offline gonut
 Post subject: Re: Recent 9x9 game
Post #25 Posted: Thu Sep 22, 2011 8:03 pm 
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For an otherwise excellent problem, a minor issue is that under AGA or Chinese rules, Black wins.

From the original position, Black defends. Under AGA rules, White then gives Black a pass stone, whereupon Black has 27 points, White has 26 points before komi. Under Chinese rules, Black's defending move doesn't decrease Black's score, so Black again is ahead by 1 on the board before komi.
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