$$Wc diagram 0 $$ | . . . . . . . . $$ | . O O . . . . . $$ | . X O . . . . . $$ | . X X O O . . . $$ | . 4 . X O . . . $$ | . O . X X O O . $$ | . O X a 1 X O . $$ | 3 X . . 2 X O . $$ | . . b . . . . . $$ +-----------------
[go]$$Wc diagram 0 $$ | . . . . . . . . $$ | . O O . . . . . $$ | . X O . . . . . $$ | . X X O O . . . $$ | . 4 . X O . . . $$ | . O . X X O O . $$ | . O X a 1 X O . $$ | 3 X . . 2 X O . $$ | . . b . . . . . $$ +-----------------[/go]
This position comes from a problem in Davis' tesuji book ( prob 8 p 137 ). Davis advises black to compromise with B2@a otherwise it is ko after W3 and B4@b. This makes me suspect that after B4 as in the diagram it is ko or worse for black. I tried to figure out why.
Here some diagrams, please correct me if I'm wrong.
$$c diagram 1 $$ | . . . . . . . . $$ | . O O . . . . . $$ | . X O . . . . . $$ | . X X O O . . . $$ | . 1 . X O . . . $$ | . O . X X O O . $$ | . O X . O X O . $$ | O X 2 5 X X O . $$ | . 3 4 . . . . . $$ +-----------------
[go]$$c diagram 1 $$ | . . . . . . . . $$ | . O O . . . . . $$ | . X O . . . . . $$ | . X X O O . . . $$ | . 1 . X O . . . $$ | . O . X X O O . $$ | . O X . O X O . $$ | O X 2 5 X X O . $$ | . 3 4 . . . . . $$ +-----------------[/go]
$$Wc 5,6 capture and recapture around 7 $$ | . . . . . . . . $$ | . O O . . . . . $$ | . X O . . . . . $$ | . X X O O . . . $$ | 0 X 4 X O . . . $$ | 2 O 3 X X O O . $$ | . O . 7 . X O . $$ | O . O X X X O . $$ | 1 . O 8 . 9 . . $$ +-----------------
[go]$$Wc 5,6 capture and recapture around 7 $$ | . . . . . . . . $$ | . O O . . . . . $$ | . X O . . . . . $$ | . X X O O . . . $$ | 0 X 4 X O . . . $$ | 2 O 3 X X O O . $$ | . O . 7 . X O . $$ | O . O X X X O . $$ | 1 . O 8 . 9 . . $$ +-----------------[/go]
$$Wc diagram 3: ko $$ | . . . . . . . . $$ | 3 O O . . . . . $$ | 1 X O . . . . . $$ | 5 X X O O . . . $$ | X X X X O . . . $$ | X O O X X O O . $$ | 2 O . O 4 X O . $$ | O . O X X X O . $$ | O . O X . O . . $$ +-----------------
[go]$$Wc diagram 3: ko $$ | . . . . . . . . $$ | 3 O O . . . . . $$ | 1 X O . . . . . $$ | 5 X X O O . . . $$ | X X X X O . . . $$ | X O O X X O O . $$ | 2 O . O 4 X O . $$ | O . O X X X O . $$ | O . O X . O . . $$ +-----------------[/go]
edit: BTW: the main problem states that w is supposed to make a sacrifice. It turns out that if B is clever he does not accept the sacrifice but compromises. So the sacrifice is virtual.