kb: On the 4-4 low approach, I recently saw this move . is normally at a.
I then (thought) I had b as sente, but he didn't reply. How to take advantage?
Andrew Grant: I've never seen in this position. When W plays here is usually played at c followed by at a, and either at b or d. After in the diagram, seems unnecessary, I'd prefer to play at b.
I think you're getting confused with this joseki, perhaps.
Dieter: And why, Andrew?
Charles Surely, if White plays here, this is the only good move?
Black has something to aim at, at p; but surely this is not yet good.
Bob McGuigan: In Joseki Genten, in the volume on starpoint joseki, Kajiwara gives this diagram as joseki in the case where Black has a stone () on the star point on the left side:
Kajiwara says that although hurts Black on the left side, takes an important point in the center and Black takes sente. But if Black wants to emphasize the left side should be at a, White responds with b, and Black plays at the point.
The pro games I have observed where 7 is played, 8 is thought to be the proper response. After white's response at 9 or where your opponent played, black has a choice between a and b. b seems to be common these days, and white will often cut immediately and there will be a fight.
The answer to your question is your decent is not sente.