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What is the Status of this corner? Is it Seki?
http://www.lifein19x19.com/viewtopic.php?f=11&t=5920		 Page 1 of 1
Author:  Charlie [ Fri May 04, 2012 12:36 am ]
Post subject:  What is the Status of this corner? Is it Seki?
What is the status of the corner shown below?

Click Here To Show Diagram Code
[go]$$Wc White to Play
$$ ------------------
$$ | . O . O . . . . .
$$ | X X X O X . . . .
$$ | . X O O X . . . .
$$ | O O O X . X . . .
$$ | . X X . . . . . .
$$ | . . . X . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .[/go]


My first instinct is that white is dead.
Author:  Txewì [ Fri May 04, 2012 12:42 am ]
Post subject:  Re: What is the Status of this corner? Is it Seki?
B can kill by filling in the outside liberties, then playing A17. If W captures at that point, B plays B18 and it's a dead shape.
Author:  blade90 [ Fri May 04, 2012 4:04 am ]
Post subject:  Re: What is the Status of this corner? Is it Seki?
Here I will explain it in more detail.

White is dead:
White can only play these 3 moves (a, b or c). But Black will ignore them all. Even if white plays all 3 white is still dead.
Click Here To Show Diagram Code
[go]$$Wc White's moves
$$ ------------------
$$ | b O a O . . . . .
$$ | X X X O X . . . .
$$ | c X O O X . . . .
$$ | O O O X . X . . .
$$ | . X X . . . . . .
$$ | . . . X . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .[/go]


Let's say white played all of the above moves and black answered by filling in the outside libertys:
Click Here To Show Diagram Code
[go]$$Wc White captures with 5
$$ ------------------
$$ | 3 O 1 O 2 . . . .
$$ | X X X O X . . . .
$$ | 5 X O O X . . . .
$$ | O O O X . X . . .
$$ | 4 X X . . . . . .
$$ | . . . X . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .[/go]


Then this is the result:
Click Here To Show Diagram Code
[go]$$Bc Since white captured with the marked stone it is black's move
$$ ------------------
$$ | O O O O X . . . .
$$ | . 1 . O X . . . .
$$ | W . O O X . . . .
$$ | O O O X . X . . .
$$ | X X X . . . . . .
$$ | . . . X . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .[/go]

Black now plays at :b1: and White is dead.
Author:  Bill Spight [ Fri May 04, 2012 8:29 am ]
Post subject:  Re: What is the Status of this corner? Is it Seki?
Obviously, if White captures Black White dies. So is it seki, or can White make it seki?

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


This, then, is the critical position. It is the only one with two shared liberties where the outside liberties are filled.

Click Here To Show Diagram Code
[go]$$Bc Dead shape
$$ ------------------
$$ | . O O O X . . . .
$$ | X B X O X . . . .
$$ | 1 X O O X . . . .
$$ | O O O X . X . . .
$$ | X X X . . . . . .
$$ | . . . X . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .[/go]


:b1: almost fills the White eye. If White captures the Black stones Black has an inside play at :bc: to kill. White is dead.
Author:  blade90 [ Fri May 04, 2012 1:01 pm ]
Post subject:  Re: What is the Status of this corner? Is it Seki?
@Bill Spight: You also need to add that black does not need to play at 'a' after white played the marked stone.
Even with outside liberties, Black does not need to play 'a'. But the fact that you can later play 'a' is the reason why it is not seki.
Click Here To Show Diagram Code
[go]$$Bc Dead shape
$$ ------------------
$$ | . O O O . . . . .
$$ | X X X O X . . . .
$$ | a X O O X . . . .
$$ | O O O X . X . . .
$$ | . X X . . . . . .
$$ | . . . X . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .[/go]
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