Here's a problem from my lunch-time game on KGS. White has just played , how should black kill? (Is it even possible to kill?)

Click Here To Show Diagram Code

[go]$$Wc Black to Respond
$$ | O X X X O . X . O O O X . X X X O . . |
$$ | X . X . X X X O O X X X O O X O . . . |
$$ | . . . X . . . X O O . X X O O . O . . |
$$ | . . . . . . . . X X . X O O O O . . . |
$$ | . . . X . . . X . , X . X X O X O O . |
$$ | . . . X . . . . X X O O X X X X X O . |
$$ | . . . . . . . X O O . . O 1 . . . X O |
$$ | . . . . . . . . . . . . . . . . . X . |
$$ +---------------------------------------+[/go]

In the game, I managed to kill white's invasion. When I went over the game, afterwards, I realised that I should have stopped it entirely, several moves earlier. I also realised that white could have lived and possibly cut off my lower-right group. In fact, I couldn't find a move for black that would prevent white from doing so.

EDIT: Also, have a look at this tsumego: http://eidogo.com/?game=1Lc8jeHa#1Lc8jeHa. The situation is similar, but black can live.

What if white plays 3 at 6?

4 at 5 works, right?

It's hard for me to prove.



There are a lot of variations from here. And maybe 5 (or 6) wasn't correct anyway.

Edit: After looking at this some more, I think white is still dead.

B looks fine to me, but I must be misreading horribly since I can't even see where the ko you mention would come from.

Click Here To Show Diagram Code

[go]$$Bc
$$ | O X X X O . X . O O O X . X X X O . . |
$$ | X . X . X X X O O X X X O O X O . . . |
$$ | . . . X . . . X O O . X X O O . O . . |
$$ | . . . . . . . . X X . X O O O O . . . |
$$ | . . . X . . . X . , X O X X O X O O . |
$$ | . . . X . . . . X X O O X X X X X O 8 |
$$ | . . . . . . . X O O . O O O X 6 4 X O |
$$ | . . . . . . . 3 9 2 X X . O 1 7 5 X . |
$$ +---------------------------------------+[/go]

Click Here To Show Diagram Code

[go]$$Bc
$$ | O X X X O . X . O O O X . X X X O . . |
$$ | X . X . X X X O O X X X O O X O . . . |
$$ | . . . X . . . X O O . X X O O . O . . |
$$ | . . . . . . . . X X . X O O O O . . . |
$$ | . . . X . . . X . , X O X X O X O O . |
$$ | . . . X . . . . X X O O X X X X X O . |
$$ | . . . . . . . X O O 8 O O O X 6 4 X O |
$$ | . . . . . . . 3 2 0 X X 9 O 1 7 5 X . |
$$ +---------------------------------------+[/go]

Four libs to three after W captures, no?

That's hard to read though. This is simpler:

Click Here To Show Diagram Code

[go]$$Wc
$$ | O X X X O . X . O O O X . X X X O . . |
$$ | X . X . X X X O O X X X O O X O . . . |
$$ | . . . X . . . X O O . X X O O . O . . |
$$ | . . . . . . . . X X . X O O O O . . . |
$$ | . . . X . . . X . , X 7 X X O X O O . |
$$ | . . . X . . . . X X O O X X X X X O . |
$$ | . . . . . . . X O O 8 5 O 1 2 . . X O |
$$ | . . . . . . . . . . 6 4 . 3 . . . X . |
$$ +---------------------------------------+[/go]

White has only two liberties and can't do a thing about it.

_________________
Memories of a sorceress girl
Endless fascination with the secrets of the world

The ko came from me overthinking the problem Somewhere in the middle of the sequence I was playing w H1 and then b G1. Obviously b would play G2 though.

I guess the best white can do is take sente to play somewhere else, and then later come back and get a ton of ko threats out of the position by threatening to live.