I'm just an 8 kyu, so my apologies if this is super obvious to stronger players!

I was looking at this tesuji in Sensei's Library today. I understand in the first example why the tesuji is necessary, because otherwise white will get 3 or more liberties and the black stones marked in the second diagram will be dead.

But I'm not seeing why the tesuji is useful in any of the other examples. For example, in this trick play, why can't black block white in a "normal" manner in the fourth diagram by playing move below (at b7) and move above (at b2), all on the second line? Why does the stronger reply require a knowledge of the "patting the raccoon's belly" tesuji?

Same question for all the other examples on the first page. Why does a simple block on the second line not work in each case? Why is it necessary to play underneath on the first line?

The trick play in the joseki is tricky; I read it for a while and I can't see why the tesuji is necessary, but all (edit: actually one) dictionnaries agree that it is. Can somebody else give it a try?

_________________
La victoire est un hasard, la défaite une nécessité.

Without the tesuji white plays both hanes, then connects the outside one: black now needs to play in the corner to stop those 4 stones dying, and then white cuts and black can't keep it all together.
(Edit: actually can he hane outside? the idea is white wants to cut on the outside and ladder the 3 stones)

As for those other examples (Segoe problem and Rin game) if you block the hane they play the other hane and if you block that one they increased their liberties from 2 to 3 in sente so take one of the three liberties of the cutting stones to win the race.

I checked Lee Changho's Hamete book, and he has the marked extra white checking extension in place when discussing this shape. In that case the 1st line tesuji is definitely needed (or else both hanes and cut at a), maybe it's not without that white stone.

Click Here To Show Diagram Code

[go]$$W
$$ ------------------
$$ | . . . . . . . . .
$$ | . . X X O . . . .
$$ | . . X O O . . . .
$$ | . . O X X . . . .
$$ | 2 . O O X . . . .
$$ | . 1 X X a . . . .
$$ | . . . . . . . . .
$$ | . . W . . . . . .
$$ | . . . . . . . . .[/go]

This was my reading. Without an extra stone I think white can't cut in time. If White doesn't connect Black captures the outside hane. As far as I get it Sensei's Library is misleading in this instance.

Click Here To Show Diagram Code

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

_________________
La victoire est un hasard, la défaite une nécessité.

It's a wiki. Y'all know what to do.

_________________
Occupy Babel!

You can get a good result without the tesuji here - just block ends up not being bad.

(So don't try this trickplay at home )

The Nihon Ki'in hamete dictionary also has the marked White stone with the following as untenable for Black. So where is the special sauce that turns this around?

Click Here To Show Diagram Code

[go]$$Wc
$$ ------------------
$$ | . . . . . . . . .
$$ | . 4 X X O . . . .
$$ | . 3 X O O . . . .
$$ | . 7 O X X . . . .
$$ | 9 6 O O X . . . .
$$ | . 1 X X 5 8 . . .
$$ | . 2 . . . . . . .
$$ | . . W . . . . . .
$$ | . . . . . . . . .[/go]

Interestingly, they also give a 'correct' line for simply playing 2 below in the original position. The diagram notes that Black's outside influence is sufficient.

Click Here To Show Diagram Code

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

_________________
Dave Sigaty
"Short-lived are both the praiser and the praised, and rememberer and the remembered..."
- Marcus Aurelius; Meditations, VIII 21

6 should be f14, and white connects out on the left and black swallows the top.

Edit: "right" should have been "left".