Pushing and crawling joseki

[PeterPeter]

$$W White to move
$$ | . . . . . . . . .
$$ | . . . , . . . . .
$$ | . . 1 b . . . . .
$$ | . . . a B . . . .
$$ | . . . O X . . . .
$$ | . . . O X . . . .
$$ | . . . O O X X . .
$$ | . . O , X O X O .
$$ | . . . . X O X . .
$$ | . . . . O O . . .
$$ | . . . . . . . . .
$$ ------------------

Click Here To Show Diagram Code

[go]$$W White to move
$$ | . . . . . . . . .
$$ | . . . , . . . . .
$$ | . . 1 b . . . . .
$$ | . . . a B . . . .
$$ | . . . O X . . . .
$$ | . . . O X . . . .
$$ | . . . O O X X . .
$$ | . . O , X O X O .
$$ | . . . . X O X . .
$$ | . . . . O O . . .
$$ | . . . . . . . . .
$$ ------------------[/go]

In this joseki, is presented as the best continuation for white. A is dismissed, on the grounds that black will start a double hane, starting at B.

If this double hane is good for black, why did he not start it at A, instead of playing his last move as shown?

(I am not memorising joseki, I am studying the ideas of pushing and crawling in the opening )

[amnal]

I'm not familiar with this line. Do you have the full sequence?

Edit: On thinking about it, it doesn't seem very good unless black has a very good reason to want the thickness a lot - white gets a lot of territory but black is undercut on the bottom and can't seal on the top. Are you sure it's supposed to be joseki? I also can't find any examples in pro games.

[Uberdude]

If this double hane is good for black, why did he not start it at A, instead of playing his last move as shown?

The joksei I know that leads to this shape, black did not play his last move as shown. In fact black passed during this joseki if white gets to jump out with . Usually black should make the thick turn instead of allowing this.

$$W Joseki part 1
$$ | . . . . . . . . .
$$ | . . . , . . . . .
$$ | . . . . . . . . .
$$ | . . . . 8 . . . .
$$ | . . . 5 6 . . . .
$$ | . . . 7 4 . . . .
$$ | . . . . 9 0 . . .
$$ | . . 1 , . . . 3 .
$$ | . . . . 2 . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ ------------------

Click Here To Show Diagram Code

[go]$$W Joseki part 1
$$ | . . . . . . . . .
$$ | . . . , . . . . .
$$ | . . . . . . . . .
$$ | . . . . 8 . . . .
$$ | . . . 5 6 . . . .
$$ | . . . 7 4 . . . .
$$ | . . . . 9 0 . . .
$$ | . . 1 , . . . 3 .
$$ | . . . . 2 . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ ------------------[/go]

$$Wm11 Joseki part 2
$$ | . . . . . . . . .
$$ | . . . , . . . . .
$$ | . . . . . . . . .
$$ | . . . 0 X . . . .
$$ | . . . O X . . . .
$$ | . . . O X . . . .
$$ | . . . 3 O X 8 . .
$$ | . . O , 2 1 4 O .
$$ | . . . . X 5 6 . .
$$ | . . . . 9 7 . . .
$$ | . . . . . . . . .
$$ ------------------

Click Here To Show Diagram Code

[go]$$Wm11 Joseki part 2
$$ | . . . . . . . . .
$$ | . . . , . . . . .
$$ | . . . . . . . . .
$$ | . . . 0 X . . . .
$$ | . . . O X . . . .
$$ | . . . O X . . . .
$$ | . . . 3 O X 8 . .
$$ | . . O , 2 1 4 O .
$$ | . . . . X 5 6 . .
$$ | . . . . 9 7 . . .
$$ | . . . . . . . . .
$$ ------------------[/go]

I suppose if sente is really important and there is something huge elsewhere that white could play to negate the thickness then black could omit , but it's a very big turn.

[PeterPeter]

I don't have the full sequence. It comes from chapter 12 of Elementary Go Series - Vol 1 - In the Beginning, by Ikuro Ishigure.

[Uberdude]

Also to answer your question, ignoring how we got here and assuming black's nobi really was his last move

If this double hane is good for black, why did he not start it at A, instead of playing his last move as shown?

Because he can't start it at A, they don't lead to the same sequence:

$$W White to move
$$ | . . . . . . . . .
$$ | . . 4 , . . . . .
$$ | . . 3 2 . . . . .
$$ | . . . 1 B . . . .
$$ | . . . O X . . . .
$$ | . . . O X . . . .
$$ | . . . O O X X . .
$$ | . . O , X O X O .
$$ | . . . . X O X . .
$$ | . . . . O O . . .
$$ | . . . . . . . . .
$$ ------------------

Click Here To Show Diagram Code

[go]$$W White to move
$$ | . . . . . . . . .
$$ | . . 4 , . . . . .
$$ | . . 3 2 . . . . .
$$ | . . . 1 B . . . .
$$ | . . . O X . . . .
$$ | . . . O X . . . .
$$ | . . . O O X X . .
$$ | . . O , X O X O .
$$ | . . . . X O X . .
$$ | . . . . O O . . .
$$ | . . . . . . . . .
$$ ------------------[/go]

This way black has a wall of 3 in the centre which is stronger than if only 2:

$$B If b hane earlier
$$ | . . . . . . . . .
$$ | . . . , . . . . .
$$ | . . 3 . . . . . .
$$ | . . 2 1 a . . . .
$$ | . . . O X . . . .
$$ | . . . O X b . . .
$$ | . . . O O X X . .
$$ | . . O , X O X O .
$$ | . . . . X O X . .
$$ | . . . . O O . . .
$$ | . . . . . . . . .
$$ ------------------

Click Here To Show Diagram Code

[go]$$B If b hane earlier
$$ | . . . . . . . . .
$$ | . . . , . . . . .
$$ | . . 3 . . . . . .
$$ | . . 2 1 a . . . .
$$ | . . . O X . . . .
$$ | . . . O X b . . .
$$ | . . . O O X X . .
$$ | . . O , X O X O .
$$ | . . . . X O X . .
$$ | . . . . O O . . .
$$ | . . . . . . . . .
$$ ------------------[/go]

The cuts at a and b will be more exciting for white when black's stone only have 2 liberties instead of 3. Also maybe white will cut directly for . Then black would have a messy fight instead of strong thickness.

[EdLee]

...more exciting for white when black's stone only have 2 liberties instead of 3.
Also maybe white will cut directly for .

Just to add to what Uberdude said...

$$B If b hane earlier
$$ | . . . . . . . . .
$$ | . . . 1 2 . . . .
$$ | . . . O X . . . .
$$ | . . . O X . . . .
$$ | . . . O O X X . .
$$ | . . O , X O X O .
$$ | . . . . X O X . .
$$ | . . . . O O . . .
$$ | . . . . . . . . .
$$ ------------------

Click Here To Show Diagram Code

[go]$$B If b hane earlier
$$ | . . . . . . . . .
$$ | . . . 1 2 . . . .
$$ | . . . O X . . . .
$$ | . . . O X . . . .
$$ | . . . O O X X . .
$$ | . . O , X O X O .
$$ | . . . . X O X . .
$$ | . . . . O O . . .
$$ | . . . . . . . . .
$$ ------------------[/go]

...for the local basic shapes,
we have W "hane'd on the head of the two stones" :

$$B
$$ | . . . . . . . . .
$$ | . . . X @ . . . .
$$ | . . . @ B . . . .
$$ | . . . @ B . . . .
$$ | . . . O @ X X . .
$$ | . . O , X O X O .
$$ | . . . . X O X . .
$$ | . . . . O O . . .
$$ | . . . . . . . . .
$$ ------------------

Click Here To Show Diagram Code

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

[Dragon Pie]

Like people have mentioned, white could cut here.

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

Click Here To Show Diagram Code

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

a is an obvious sente move that threatens to capture two black stones. If black protects against that extension in some way, black's cutting stone will remain weak and in being forced to strengthen himself, white will become stronger on the outside and this will mute black's thickness. Since black's aim is thickness in playing this joseki, that's not desirable.

Other than the obvious forcing move against the two stones, things could proceed something like this and white would have a forcing move at 4. Black's thickness is greatly reduced with a variation like this:

$$B
$$ | . . . 3 . . . . .
$$ | . . . . 2 . . . .
$$ | . . 1 B W . . . .
$$ | . . . O X . 4 . .
$$ | . . . O X . . . .
$$ | . . . O O X X . .
$$ | . . O , X O X O .
$$ | . . . . X O X . .
$$ | . . . . O O . . .
$$ | . . . . . . . . .
$$ ------------------

Click Here To Show Diagram Code

[go]$$B
$$ | . . . 3 . . . . .
$$ | . . . . 2 . . . .
$$ | . . 1 B W . . . .
$$ | . . . O X . 4 . .
$$ | . . . O X . . . .
$$ | . . . O O X X . .
$$ | . . O , X O X O .
$$ | . . . . X O X . .
$$ | . . . . O O . . .
$$ | . . . . . . . . .
$$ ------------------[/go]

At which point, a move like a would be something for white to aim for and a move on the right side would also attack the other black stones.

$$B
$$ | . . a . . . . . .
$$ | . . . . . . . . .
$$ | . . . 3 . . . . .
$$ | . . . . 2 . . . .
$$ | . . 1 B W . . . .
$$ | . . . O X . 4 . .
$$ | . . . O X . . . .
$$ | . . . O O X X . .
$$ | . . O , X O X O .
$$ | . . . . X O X . .
$$ | . . . . O O . . .
$$ | . . . . . . . . .
$$ ------------------

Click Here To Show Diagram Code

[go]$$B
$$ | . . a . . . . . .
$$ | . . . . . . . . .
$$ | . . . 3 . . . . .
$$ | . . . . 2 . . . .
$$ | . . 1 B W . . . .
$$ | . . . O X . 4 . .
$$ | . . . O X . . . .
$$ | . . . O O X X . .
$$ | . . O , X O X O .
$$ | . . . . X O X . .
$$ | . . . . O O . . .
$$ | . . . . . . . . .
$$ ------------------[/go]

Does this give you an idea of why the double hane at this point would be an overplay?

Still, don't forget about the play. It's possible that this play could be a good one if black is strong on the outside and has supporting stones to help his otherwise weak groups. It does essentially seal white in and it could lead to black developing on both sides if his groups are strong enough and white's cutting stones could even become a target for an attack if black is very strong on the outside, so it's good to remember that sometimes non-joseki moves are correct moves depending on the situation.