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 Post subject: Interesting go problem from a real game
Post #1 Posted: Thu Sep 01, 2016 10:19 pm 
Dies with sente

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I recently came across an interesting game in one of the online tournaments:

Click Here To Show Diagram Code
[go]$$B
$$ ----------------------
$$ X . X X O . . . . . . |
$$ . X . X O . X X W . . |
$$ X X X O O . . O X . . |
$$ . . . . O . . O X . . |
$$ X X . O X X . O X O . |
$$ . X O . . . O O O X . |
$$ O O O X X X O X X . X |
$$ . O X X . O . O X X X |
$$ . . . . X O . O . O X |
$$ . . . . X O O . O . O |
$$ . . . . X X X O . O . |
$$[/go]


The question is, after white's move, can black defend the corner without a ko?

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 Post subject: Re: Interesting go problem from a real game
Post #2 Posted: Fri Sep 02, 2016 3:10 am 
Lives with ko

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Click Here To Show Diagram Code
[go]$$W
$$ ----------------------
$$ X . X X O . . . X . . |
$$ . X . X O . X X X X 3 |
$$ X X X O O . . O X O . |
$$ . . . . O . . O X O 1 |
$$ X X . O X X . O X O 4 |
$$ . X O . . . O O O X 2 |
$$ O O O X X X O X X . X |
$$ . O X X . O . O X X X |
$$ . . . . X O . O . O X |
$$ . . . . X O O . O . O |
$$ . . . . X X X O . O . |
$$[/go]


I think so

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 Post subject: Re: Interesting go problem from a real game
Post #3 Posted: Fri Sep 02, 2016 3:16 am 
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dhu163 wrote:
Click Here To Show Diagram Code
[go]$$W
$$ ----------------------
$$ X . X X O . . . X . . |
$$ . X . X O . X X X X 3 |
$$ X X X O O . . O X O . |
$$ . . . . O . . O X O 1 |
$$ X X . O X X . O X O 4 |
$$ . X O . . . O O O X 2 |
$$ O O O X X X O X X . X |
$$ . O X X . O . O X X X |
$$ . . . . X O . O . O X |
$$ . . . . X O O . O . O |
$$ . . . . X X X O . O . |
$$[/go]


Click Here To Show Diagram Code
[go]$$W
$$ ----------------------
$$ X . X X O . . . . . . |
$$ . X . X O . X X 1 2 . |
$$ X X X O O . . O X . . |
$$ . . . . O . . O X . 3 |
$$ X X . O X X . O X O . |
$$ . X O . . . O O O X . |
$$ O O O X X X O X X . X |
$$ . O X X . O . O X X X |
$$ . . . . X O . O . O X |
$$ . . . . X O O . O . O |
$$ . . . . X X X O . O . |
$$[/go]

Ko. I don't see any way for Black to keep the whole corner, at least the 2 stones on top are going to get ko'd.


This post by Shaddy was liked by 2 people: dhu163, gamesorry
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 Post subject: Re: Interesting go problem from a real game
Post #4 Posted: Fri Sep 02, 2016 3:19 am 
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Edit : same idea as Shaddy

White won't play like that in this line :
Click Here To Show Diagram Code
[go]$$B
$$ ----------------------
$$ X . X X O . . . 3 . . |
$$ . X . X O . X X W 1 . |
$$ X X X O O . . O X 2 . |
$$ . . . . O . . O X . 4 |
$$ X X . O X X . O X O . |
$$ . X O . . . O O O X . |
$$ O O O X X X O X X . X |
$$ . O X X . O . O X X X |
$$ . . . . X O . O . O X |
$$ . . . . X O O . O . O |
$$ . . . . X X X O . O . |
$$[/go]

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 Post subject: Re: Interesting go problem from a real game
Post #5 Posted: Fri Sep 02, 2016 10:57 am 
Oza

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Online playing schedule: When my wife is out.
The empty triangle looks good to me at first, but...
Click Here To Show Diagram Code
[go]$$B
$$ ----------------------
$$ X . X X O . . . . . . |
$$ . X . X O . X X W 2 3 |
$$ X X X O O . . O X 1 6 |
$$ . . . . O . . O X . 4 |
$$ X X . O X X . O X O . |
$$ . X O . . . O O O X 5 |
$$ O O O X X X O X X . X |
$$ . O X X . O . O X X X |
$$ . . . . X O . O . O X |
$$ . . . . X O O . O . O |
$$ . . . . X X X O . O . |
$$[/go]


However, does black need to play :b3?

Click Here To Show Diagram Code
[go]$$B
$$ ----------------------
$$ X . X X O . 8 6 9 7 0 |
$$ . X . X O . X X W 2 4 |
$$ X X X O O . . O X 1 . |
$$ . . . . O . . O X . 3 |
$$ X X . O X X . O X O 5 |
$$ . X O . . . O O O X . |
$$ O O O X X X O X X . X |
$$ . O X X . O . O X X X |
$$ . . . . X O . O . O X |
$$ . . . . X O O . O . O |
$$ . . . . X X X O . O . |
$$[/go]


This seems to work:
Click Here To Show Diagram Code
[go]$$B
$$ ----------------------
$$ X . X X O . O O 1 . O |
$$ . X . X O . X X O O O |
$$ X X X O O . . O X X . |
$$ . . . . O . . O X . X |
$$ X X . O X X . O X O X |
$$ . X O . . . O O O X . |
$$ O O O X X X O X X . X |
$$ . O X X . O . O X X X |
$$ . . . . X O . O . O X |
$$ . . . . X O O . O . O |
$$ . . . . X X X O . O . |
$$[/go]

However:
Click Here To Show Diagram Code
[go]$$B
$$ ----------------------
$$ X . X X O . . 7 . 6 . |
$$ . X . X O . X X W 2 4 |
$$ X X X O O . 8 O X 1 . |
$$ . . . . O . . O X . 3 |
$$ X X . O X X . O X O 5 |
$$ . X O . . . O O O X . |
$$ O O O X X X O X X . X |
$$ . O X X . O . O X X X |
$$ . . . . X O . O . O X |
$$ . . . . X O O . O . O |
$$ . . . . X X X O . O . |
$$[/go]

So perhaps:
Click Here To Show Diagram Code
[go]$$B
$$ ----------------------
$$ X . X X O . . 9 . 6 . |
$$ . X . X O . X X W 2 4 |
$$ X X X O O . 7 O X 1 . |
$$ . . . . O . 8 O X . 3 |
$$ X X . O X X . O X O 5 |
$$ . X O . . . O O O X . |
$$ O O O X X X O X X . X |
$$ . O X X . O . O X X X |
$$ . . . . X O . O . O X |
$$ . . . . X O O . O . O |
$$ . . . . X X X O . O . |
$$[/go]

And now black has enough liberties for the fight.

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 Post subject: Re: Interesting go problem from a real game
Post #6 Posted: Fri Sep 02, 2016 11:34 am 
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skydyr - still not enough liberties.

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 Post subject: Re: Interesting go problem from a real game
Post #7 Posted: Fri Sep 02, 2016 12:18 pm 
Oza

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Shaddy wrote:
skydyr - still not enough liberties.


In the last diagram? I don't see it, so could you explain?

That said, I think on re-examination, white can play at :b9: instead and black can either play an unfavourable ko or connect and let white connect under.

Edit: Nevermind, I'm still counting four for some reason.

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 Post subject: Re: Interesting go problem from a real game
Post #8 Posted: Sun Sep 11, 2016 3:51 pm 
Lives with ko

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Click Here To Show Diagram Code
[go]$$W
$$ ----------------------
$$ X . X X O . . . 6 . . |
$$ . X . X O . X X 1 2 . |
$$ X X X O O . . O X 5 . |
$$ . . . . O . . O X . 3 |
$$ X X . O X X . O X O . |
$$ . X O . . . O O O X 4 |
$$ O O O X X X O X X . X |
$$ . O X X . O . O X X X |
$$ . . . . X O . O . O X |
$$ . . . . X O O . O . O |
$$ . . . . X X X O . O . |
$$[/go]

Click Here To Show Diagram Code
[go]$$W
$$ ----------------------
$$ X . X X O . . . X . . |
$$ . X . X O . X X 2 X 1 |
$$ X X X O O . . O X O . |
$$ . . . . O . . O X . O |
$$ X X . O X X . O X O . |
$$ . X O . . . O O O X X |
$$ O O O X X X O X X . X |
$$ . O X X . O . O X X X |
$$ . . . . X O . O . O X |
$$ . . . . X O O . O . O |
$$ . . . . X X X O . O . |
$$[/go]

now what for white?

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 Post subject: Re: Interesting go problem from a real game
Post #9 Posted: Sun Sep 11, 2016 4:44 pm 
Dies with sente

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Phillip:

Click Here To Show Diagram Code
[go]$$W
$$ ----------------------
$$ X . X X O . . . X . . |
$$ . X . X O . X X . X . |
$$ X X X O O . . O X O . |
$$ . . . . O . . O X a O |
$$ X X . O X X . O X O b |
$$ . X O . . . O O O X X |
$$ O O O X X X O X X . X |
$$ . O X X . O . O X X X |
$$ . . . . X O . O 1 O X |
$$ . . . . X O O . O . O |
$$ . . . . X X X O . O . |
$$[/go]


Black is captured, because he cant approach a, so white b next captures.

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 Post subject: Re: Interesting go problem from a real game
Post #10 Posted: Mon Sep 12, 2016 12:46 am 
Dies with sente

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Thanks, so it does seem that a ko is unavoidable.

FYI, the original game is here. I missed white's refusal at (4,1) at first glance.

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 Post subject: Re: Interesting go problem from a real game
Post #11 Posted: Mon Sep 12, 2016 10:18 pm 
Beginner

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Schachus wrote:
Phillip:

Click Here To Show Diagram Code
[go]$$W
$$ ----------------------
$$ X . X X O . . . X . . |
$$ . X . X O . X X . X . |
$$ X X X O O . . O X O . |
$$ . . . . O . . O X a O |
$$ X X . O X X . O X O b |
$$ . X O . . . O O O X X |
$$ O O O X X X O X X . X |
$$ . O X X . O . O X X X |
$$ . . . . X O . O 1 O X |
$$ . . . . X O O . O . O |
$$ . . . . X X X O . O . |
$$[/go]


Black is captured, because he cant approach a, so white b next captures.
I still don't get why black dies. Wouldn't 5 below save black if white played as expected above?
Click Here To Show Diagram Code
[go]$$B
$$ ----------------------
$$ X . X X O . . . 3 . . |
$$ . X . X O . X X . 1 5 |
$$ X X X O O . . O X 2 . |
$$ . . . . O . . O X . 4 |
$$ X X . O X X . O X O . |
$$ . X O . . . O O O X . |
$$ O O O X X X O X X . X |
$$ . O X X . O . O X X X |
$$ . . . . X O . O 6 O X |
$$ . . . . X O O . O . O |
$$ . . . . X X X O . O . |
$$[/go]

Edit: oh, right, it still ends in ko

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