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Offline speedchase
 Post subject: another Tsumego question
Post #1 Posted: Tue Jan 03, 2012 7:42 pm 
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Click Here To Show Diagram Code
[go]$$B
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . X . . .
$$ - . X X X . X . . .
$$ - . X O X . . X . .
$$ - O O O O b O X . X
$$ - . X O . a . . . .
$$ ---------------------[/go]


The solution given is a, but I don't see why b doesn't work.
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Offline Kirby
 Post subject: Re: another Tsumego question
Post #2 Posted: Tue Jan 03, 2012 7:56 pm 
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b works, too.

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Offline speedchase
 Post subject: Re: another Tsumego question
Post #3 Posted: Tue Jan 03, 2012 8:07 pm 
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Thanks you Kirby!
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Offline tchan001
 Post subject: Re: another Tsumego question
Post #4 Posted: Tue Jan 03, 2012 8:13 pm 
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b works BUT it is not the best solution as it allows black to get an extra ko threat. a is settled plain and simple.

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Offline speedchase
 Post subject: Re: another Tsumego question
Post #5 Posted: Tue Jan 03, 2012 8:21 pm 
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Click Here To Show Diagram Code
[go]$$B :b7: at :b1:
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . X . . .
$$ - . X X X . X . . .
$$ - . X O X 2 5 X . .
$$ - O O O O 1 O X . X
$$ - . X O 6 3 4 . . .
$$ ---------------------[/go]


w has 3 threats


Click Here To Show Diagram Code
[go]$$B :b7: at :b3:
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . X . . .
$$ - . X X X . X . . .
$$ - . X O X 4 5 X . .
$$ - O O O O 3 O X . X
$$ - . X O 6 1 2 . . .
$$ ---------------------[/go]


w has 3 threats


What am I missing?
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Offline Kirby
 Post subject: Re: another Tsumego question
Post #6 Posted: Tue Jan 03, 2012 8:22 pm 
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tchan001 wrote:
b works BUT it is not the best solution as it allows black to get an extra ko threat. a is settled plain and simple.


I agree that 'a' seems more natural, but I'm having trouble verifying this statement.

If we play 'a', I see that there can be three ko threats:
Click Here To Show Diagram Code
[go]$$W Ko threat #1
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . X . . .
$$ - . X X X . X . . .
$$ - . X O X . . X . .
$$ - O O O O . O X . X
$$ - . X O . B 1 . . .
$$ ---------------------[/go]


Click Here To Show Diagram Code
[go]$$B Ko threat #2
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . X . . .
$$ - . X X X . X . . .
$$ - . X O X 2 . X . .
$$ - O O O O X O X . X
$$ - . X O . X O . . .
$$ ---------------------[/go]


Click Here To Show Diagram Code
[go]$$W Ko threat #3
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . X . . .
$$ - . X X X . X . . .
$$ - . X O X O X X . .
$$ - O O O O C O X . X
$$ - . X O 3 C O . . .
$$ ---------------------[/go]


On the other hand, if we play 'b', I see a similar count:
Click Here To Show Diagram Code
[go]$$W Ko threat #1
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . X . . .
$$ - . X X X . X . . .
$$ - . X O X 1 . X . .
$$ - O O O O B O X . X
$$ - . X O . . . . . .
$$ ---------------------[/go]


Click Here To Show Diagram Code
[go]$$B Ko threat #2
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . X . . .
$$ - . X X X . X . . .
$$ - . X O X O . X . .
$$ - O O O O X O X . X
$$ - . X O . X 2 . . .
$$ ---------------------[/go]


Click Here To Show Diagram Code
[go]$$W Ko threat #3
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . X . . .
$$ - . X X X . X . . .
$$ - . X O X O X X . .
$$ - O O O O C O X . X
$$ - . X O 3 C O . . .
$$ ---------------------[/go]

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Offline Kirby
 Post subject: Re: another Tsumego question
Post #7 Posted: Tue Jan 03, 2012 8:25 pm 
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The benefit that I can see is that if, later in the game, something else is bigger than killing this shape.

If we have played 'a':
Click Here To Show Diagram Code
[go]$$B
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . X . . .
$$ - . X X X . X . . .
$$ - . X O X . . X . .
$$ - O O O O . O X . X
$$ - . X O . B . . . .
$$ ---------------------[/go]


Then if white threatens life, and black lets him have it, there's not a ton of loss:
Click Here To Show Diagram Code
[go]$$B
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . X . . .
$$ - . X X X . X . . .
$$ - . X O X . . X . .
$$ - O O O O O O X . X
$$ - . X O . X O . . .
$$ ---------------------[/go]


But in the same scenario, there seems to be more of a loss if we had done 'b':
Click Here To Show Diagram Code
[go]$$B
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . X . . .
$$ - . X X X . X . . .
$$ - . X O X O . X . .
$$ - O O O O C O X . X
$$ - . X O . O . . . .
$$ ---------------------[/go]


I think that's why 'a' seems more natural to me.

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Offline speedchase
 Post subject: Re: another Tsumego question
Post #8 Posted: Tue Jan 03, 2012 8:31 pm 
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Unless you are worried about black's thickness I would think it would be the opposite. In the first variation white's group is unconditionally alive with 6 points. In the second variation whites group is unconditionally alive with 5 points including the prisoner with a 1 point gote play to get the sixth. Is the security of blacks thickness really threatened enough for the difference to be more than 1/2 a point?
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Offline Kirby
 Post subject: Re: another Tsumego question
Post #9 Posted: Tue Jan 03, 2012 9:17 pm 
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speedchase wrote:
Unless you are worried about black's thickness I would think it would be the opposite. In the first variation white's group is unconditionally alive with 6 points. In the second variation whites group is unconditionally alive with 5 points including the prisoner with a 1 point gote play to get the sixth. Is the security of blacks thickness really threatened enough for the difference to be more than 1/2 a point?


Both groups end in gote, but white can more easily get another point, I think:

Click Here To Show Diagram Code
[go]$$B Diagram A
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . . . . .
$$ - . . . . . X . . .
$$ - . X X X p X . . .
$$ - . X O X C . X . .
$$ - O O O O O O X . X
$$ - . X O . X O . . .
$$ ---------------------[/go]


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


In Diagram A, black can play at the marked intersection to get the point at "p". In Diagram B, on the other hand, this point is already taken away by the marked white stone, so black has no chance of getting the point at "p". White can later play at "q" to gain another point for his group.

In other words, because "p" is not an option in Diagram B, and because white's play at "p" is sente, and because white can play at "q", I feel like white gains more in Diagram B.

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Offline speedchase
 Post subject: Re: another Tsumego question
Post #10 Posted: Tue Jan 03, 2012 9:18 pm 
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Oh I see that makes sense.
Thanks guys!
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Offline Kirby
 Post subject: Re: another Tsumego question
Post #11 Posted: Tue Jan 03, 2012 9:20 pm 
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speedchase wrote:
Oh I see that makes sense.
Thanks guys!


Cool... Because it only partially makes sense to me. I'm still kind of thinking about it. :D

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