lapos wrote:
@Bill Spight: But how white could create a mini chinese without a stone in d17 ?
You are right, of course.

But I hope I got the idea across that White could approach the top left corner and then make a formation spanning the left side.
Besides, I never play the two space high pincer. Maybe I should learn the basic joseki

Don't let ignorance of joseki prevent you from making the right play.
Do not you think that

in O17 make my group a little thin?
Both the two space extension (to N-17) and the three space extension are standard. However, the two space extension does not have a very good follow-up. The three space extension does (such as P-15). If White had had a stone on Q-15 instead of R-15 the two space extension would have been better.
I prefer the attacking variation to either extension, though.
Why

was unnecessary ? It seemed to prevent a linkage between the white weak group and it was sente.
White cannot connect. He can only threaten to connect.
But that raises an interesting question. Is

a double sente? Each player has a big threat. Let us look at the threat to connect more closely.
If White connects, he lives in the corner and there is no more attack on the group on the top side. That's pretty good. Two birds with one stone.

Except it's two stones.

That is, two moves.
Suppose that White does not make the threat to connect and play goes on while White fends off the attack. Then the threat to connect is meaningless, and Black has a small sente against the corner. Now suppose that the attack is successful and the group dies. Then White's threat to connect really is double sente and Black will wish that he had threatened the corner with sente first.
In the current state, is it double sente? No, it is not. Why not? Because while White plays two stones to connect, Black will make two big moves, gaining much more than the connection does. So

is not necessary.
Still, is it worth it for Black to play his sente against the corner, to guard against it becoming double sente? Better safe than sorry.
That was pretty much Sakata's thinking in similar situations. Among pros, he was one who played kikashi early. Takagawa was the opposite. He played kikashi only when it was absolutely necessary. And since the two were rivals, in many of their games you can see the tension between these two ideas of when to play kikashi. Sometimes Takagawa paid the price for not playing kikashi early enough, and lost the chance.
In this case, sente against the corner is a certain kind of kikashi, called kikashi without loss. That is, the kikashi against the corner does not destroy other gainful alternatives for Black. And, while Black does not fear an immediate threat to connect by White, it is possible for the fighting to develop so that the kikashi is lost. In a way, that's not so bad, because it would mean that Black had killed the White group on the side. Still, there is an argument for taking the kikashi soon.