3-3 point invasion query 9

tderz: It is a method for Black to get sente.
[1] Important is the stretch . If crawls, Black does not have to respond immedeately locally and gets global sente.
The cutting point at c is protected, because Black has also more liberties (around d).

The more "usual"(?) variation on the right ends in gote after white a, Black b.

I just see that unkx added already a continuation,
however, in ^[2] could be at here in ^[1].

Of course, Black could also wait (as in Zhang Wendong vs. Zhou Heyang 1992-09-14) and decide later whether to hane at or nobi .

Having checked gobase, I get the impression, that the continuation following my reasoning is played least often.
White playing d himself, with Black replying at e occurs often, as does the simple (?) Black f for (=unkx80's variation below).

My summary could be: if White crawls with – take sente.

unkx80: I think this is joseki.[2]