What about this Alphago Joseki?

[Leon]

Hi, I have a hard time figuring out why black doesnt play the following exchange in this joseki. Does anyone have an idea?

$$B
$$ , . . . . . , . . . |
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ . . . . . . . X . . |
$$ . . . . . . O . X . |
$$ , . . . . . O X . . |
$$ . . . . O . W O X . |
$$ . . . . . . O B . . |
$$ . . . . . . . . . . |
$$ --------------------+

Click Here To Show Diagram Code

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

[Tryss]

If black play this now, white can probably tenuki : if black capture

$$B
$$ , . . . . . , . . . |
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ . . . . . . . X . . |
$$ . . . . . . O . X . |
$$ , . . . . . O X . . |
$$ . . . . O 2 1 . X . |
$$ . . . . . . O X . . |
$$ . . . . . . . . . . |
$$ --------------------+

Click Here To Show Diagram Code

[go]$$B
$$ , . . . . . , . . . |
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ . . . . . . . X . . |
$$ . . . . . . O . X . |
$$ , . . . . . O X . . |
$$ . . . . O 2 1 . X . |
$$ . . . . . . O X . . |
$$ . . . . . . . . . . |
$$ --------------------+[/go]

Is this worth giving up a move to white in the openning?

[Uberdude]

That's a tricky timing question indeed! I think white will generally connect to keep the black group not alive. There are some downsides to the atari without the answer being white tenukis to a bigger place: by connecting the 2 white stones above get more liberties so future moves lose some effectiveness e.g. Black 8 here has an atari at a as followup so is a better move now (semi sente) than if Black had played corner atari.

$$W
$$ , . . . . . , . . . |
$$ . . . . . . . . . . |
$$ . . . . . 7 . 1 . . |
$$ . . . . . . . . 5 . |
$$ . . . . . . 2 X 6 . |
$$ . . . . . 8 O 3 X . |
$$ , . . . . a O X 4 . |
$$ . . . . O . . O X . |
$$ . . . . . . O . . . |
$$ . . . . . . . . . . |
$$ --------------------+

Click Here To Show Diagram Code

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

[Uberdude]

This double inside approach and funny hanging connection is popular these days, in Chinese league round 18 yesterday Mi Yuting vs Xie Erhao: http://www.go4go.net/go/games/sgfview/77733.

[mipli]

In-Seong recently had a lecture on just this shape.

$$B
$$ . . . . . . . . .
$$ . . . . . a . . .
$$ . . . . . . . . .
$$ . . . . . 7 X . .
$$ . . . . . 6 . 5 .
$$ . . . . . O 1 . .
$$ . . . O . . 2 3 .
$$ . . . . . 4 b . .
$$ . . . . . . . . .
$$ -----------------

Click Here To Show Diagram Code

[go]$$B
$$ . . . . . . . . .
$$ . . . . . a . . .
$$ . . . . . . . . .
$$ . . . . . 7 X . .
$$ . . . . . 6 . 5 .
$$ . . . . . O 1 . .
$$ . . . O . . 2 3 .
$$ . . . . . 4 b . .
$$ . . . . . . . . .
$$ -----------------[/go]

One reason he mentioned for choosing this variation as white was that the extra liberty for white makes the push at less powerful, so white can tenuki - often to invade/reduce somewhere on the right hand side which black is probably trying to build. Because of this black would rather play at A, or tenuki as in the game you linked to.