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

Question

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)

Answer 1

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.