I recently had this corner position as black, and I now know the worst possible way to think about it: assume the corner has been killed, and only after w takes the 4 stones, to think it's a ko that I don't automatically win, then after the ko starts to ignore his threat at a and then watch my stones die. I suppose my failure to examine the corner was fueled by vaguely remembering that in Japanese rules, a bent 4 in the corner (with no outside liberties and no unremovable ko threats - forgot that) is dead. After looking at Senseis library, it turns out that my misconception was even worse, because without having filled the outside liberties, white is unconditionally alive (w can capture the 4 stones then crush whatever b plays. So this post is just a memento to a disaster that I hope won't happen again soon.

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[go]$$B bent 4 in the corner. Diagram made at: http://hiddema.nl/diagrammer/
$$ +---------------------------------------+
$$ | X X X O . X O . . . . . . . . . . . . |
$$ | X O . O . X O . . . . . . . . . . . . |
$$ | O O O O X X O . . . O . . . . . . . . |
$$ | . X X , X O O . . , . . . . . , . . . |
$$ | . . X . X O . . . . . . . . . . . . . |
$$ | . X X a . O . . . . . . . . . . . . . |
$$ | O O O X X . . . . . . . . . . . . . . |
$$ | . . O O . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . O . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ +---------------------------------------+[/go]

_________________
Patience, grasshopper.

When we talk about bent four in the corner it's often a shape which can be turned into a bent four, as below. If white has outside liberties then you don't want to turn it into one yet because it allows white to live by the crush, you only want to do so once the liberties are filled. It might help to think of it like a temporary seki: you don't want to start action on the inside with b because that allows the corner to live, but neither can the opponent live if he plays first.

Click Here To Show Diagram Code

[go]$$B bent 4 in the corner. Diagram made at: http://hiddema.nl/diagrammer/
$$ +---------------------------------------+
$$ | X X X O . X O . . . . . . . . . . . . |
$$ | b O . O . X O . . . . . . . . . . . . |
$$ | O O O O X X O . . . O . . . . . . . . |
$$ | . X X , X O O . . , . . . . . , . . . |
$$ | . . X . X O . . . . . . . . . . . . . |
$$ | . X X a . O . . . . . . . . . . . . . |
$$ | O O O X X . . . . . . . . . . . . . . |
$$ | . . O O . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . O . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ +---------------------------------------+[/go]

Thanks for that clarification Uberdude. In essence, the position I showed wasn't a bent 4 in the corner at all.

_________________
Patience, grasshopper.

Its topic was 'internal liberty shortage'.

Click Here To Show Diagram Code

[go]$$B
$$ +---------------------------------------+
$$ | . X O O . X O . . . . . . . . . . . . |
$$ | X O O O . X O . . . . . . . . . . . . |
$$ | O O O O X X O . . . O . . . . . . . . |
$$ | X X X X X O O . . , . . . . . , . . . |
$$ | . . X . X O . . . . . . . . . . . . . |
$$ | . X X a . O . . . . . . . . . . . . . |
$$ | O O O X X . . . . . . . . . . . . . . |
$$ | . . O O . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . O . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |[/go]

Insofar as this is a reference to the underlying Japanese form, a problem is that the term refers to the intersections not the stones. Bent four refers to four empty points.

We get the same problem with e.g. sanmoku nakade, which too many people take to refer to a three-stone nakade shape. Again, no. It means three empty points where you can play a nakade - a move in the middle. Moku has some confusing usages, not to mention the character having different readings, which is one more reason to frown on the Hikaru babes (mis)using the term.

Snap...

No Mister Bond, I expect you to ... Ko? WTF!

Click Here To Show Diagram Code

[go]$$B Moves 213 to 217
$$ ---------------------------------------
$$ | . . . . . . . . . . O O O X . . . . . |
$$ | . X O O O . . . . . O . O X X . . . . |
$$ | . X X O X O . . O . O . . O X . . . . |
$$ | . X O O X O . O . O . O . O X X . . . |
$$ | . X O X X X O O X . . O . O O . X . . |
$$ | . . X X O O O X . X . O . O . O X . . |
$$ | . . . X O X X X . . . O O X O X . X . |
$$ | X . . X O X . X . O X X X X O X . X . |
$$ | O X X X X . . X . O X . . X O . X X . |
$$ | O O X O O X X X X O X . X X . O X . X |
$$ | . O O . . O O O O O X X . . X O O X X |
$$ | . . . . . . . . . . O X X X O . O O X |
$$ | . . . O O . . . . . O X . O . . . O X |
$$ | . O O X X X X X O . . O X X O . . . O |
$$ | . O X . . . . O . . . O . . O O . . O |
$$ | O O X X . . X O . , . . . O X 2 O O X |
$$ | O X X . . X X O . . . . O X X X O X 1 |
$$ | X X . . . . X O . O . . O O X 3 X X . |
$$ | . . . . . . X X O . . . . O O X . 4 5 |
$$ ---------------------------------------[/go]

It was bent four in the corner, but it wasn't Bent Four in the Corner.

_________________
The Adkins Principle:
At some point, doesn't thinking have to go on?
— Winona Adkins

Visualize whirled peas.

Everything with love. Stay safe.