Deviation of 3-3 invasion - how to live/kill?

I know the following is joseki for an approach of the 4-4 stone followed by a 3/3 invasion...

$$cm1 A normal 3/3 invasion joseki (incomplete)$$ +---------------------------------------+
$$| . . . . . . . . . . . . . . . . . . . |$$ | . . . . . . . . . . . . . . . . . . . |
$$| . 7 3 . . 2 . . . . . . . . . . . . . |$$ | . 5 4 O . . . . . , . . . . . , . . . |
$$| . 6 8 . . . . . . . . . . . . . . . . |$$ | . . 1 . . . . . . . . . . . . . . . . |
$$| . . . . . . . . . . . . . . . . . . . |  .. and this is a possible continuation: $$cm1 Continuation of the joseki
$$+---------------------------------------+$$ | . . . . . . . . . . . . . . . . . . . |
$$| . . . 7 . . . . . . . . . . . . . . . |$$ | . X X 1 2 O . . . . . . . . . . . . . |
$$| . X O O . . . . . , . . . . . , . . . |$$ | 4 O O . 6 . . . . . . . . . . . . . . |
$$| . 3 X 5 . . . . . . . . . . . . . . . |$$ | . . . . . . . . . . . . . . . . . . . |


If I understand correctly, a white move at E18 has to be answered by black, or white A16 kills. Eidogo lists only black 7 as above at this point. It does not list the following variation, hence, I assume it is somehow bad for black, but I am not sure why.

$$cm1 Deviation from joseki$$ +---------------------------------------+
$$| . . . . . . . . . . . . . . . . . . . |$$ | . . . 3 1 2 . . . . . . . . . . . . . |
$$| . X X X O O . . . . . . . . . . . . . |$$ | . X O O . . . . . , . . . . . , . . . |
$$| O O O . O . . . . . . . . . . . . . . |$$ | . X X X . . . . . . . . . . . . . . . |
$$| . . . . . . . . . . . . . . . . . . . |  • Am I correct that black is alive like that? If not, please show how to kill black. • Given that black is alive in both variants, why would one prefer the default variant? I first thought that 7 may be sente, but with E18 threatening to kill it seems gote just as well, while getting fewer points? (I'm sorry if this is a duplicate question, but I have no idea how to search a stackexchange site for go-deviations really) - I believe playing 3 at D19 in the deviation would let the corner live unconditionally. – goldPseudo Jan 23 '12 at 2:26 We do not yet have a good way to search for specific positions or joseki sadly ;( Btw, I see this is your first question here (and already really well formatted!), so welcome on Board and Card Games :) – mafutrct Jan 23 '12 at 12:03 1 Answer In the deviated form, white can play at B18 and the corner will live or die as a ko, or it can end up in seki. Even if black has more than enough ko threats to win the battle, it is unlikely ever worth it. $$Wcm4 Continuation of deviation: Ko
$$+---------------------------------------+$$ | 7 . 3 6 5 . . . . . . . . . . . . . . |
$$| 2 1 a X X O . . . . . . . . . . . . . |$$ | . X X X O O . . . . . . . . . . . . . |
$$| 4 X O O . . . . . , . . . . . , . . . |$$ | O O O . O . . . . . . . . . . . . . . |
$$| . X X X . . . . . . . . . . . . . . . |$$ | . . . . . . . . . . . . . . . . . . . |


The corner lives or dies depending on who wins the two stage ko; black's normal defense of playing 7 at a won't work due to a shortage of liberties.

Alternatively, if white does not have sufficient ko threats the whole corner could end up as a seki as follows:

$$Wcm4 Continuation of deviation: Seki$$ +---------------------------------------+
$$| 8 a 3 6 5 7 . . . . . . . . . . . . . |$$ | 2 1 . X X O . . . . . . . . . . . . . |
$$| . X X X O O . . . . . . . . . . . . . |$$ | 4 X O O . . . . . , . . . . . , . . . |
$$| O O O . O . . . . . . . . . . . . . . |$$ | . X X X . . . . . . . . . . . . . . . |
 | . . . . . . . . . . . . . . . . . . . |


Note that in this variation, black can choose to start the same ko by playing 11 at a instead.

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In the first example, black 5 looks like a mistake. What happens if black responds at White 8? I see White C19, Black A16, White A18, Black B19, White A19, Black C18 for seki. White can still force a ko by playing A18 at A19, but now it's an approach ko for white. And no longer two step. –  OmnipotentEntity Jan 23 '12 at 22:41
@OmnipotentEntity: White avoids the approach ko with A16 instead of C19. I believe the best black can hope for there is a direct ko with white capturing first. –  goldPseudo Jan 23 '12 at 23:37
Well, you have my vote. :) –  OmnipotentEntity Jan 24 '12 at 2:04