This is a common way to develop a 4-4 point in the corner.
This is the main variation of White's 3-3 invasion of the enclosure. may also be played at
(see below).
For at
see 4473 enclosure 3-3 invasion, block on inner side.
This is the standard line, and White ends in sente. The White group is an L+2-group and is alive. Black though has considerable influence now.
Variants:
Black may also play this way. Then
(or a) lives.
here is proper, but may be omitted: if Black wants to end in sente here it may make sense to play
in this manner, rather than follow the above main variation.
Dieter: Question. at a reduces the corner to an L+1-group, whose status depends on sente. So Black can play a in sente ?
Here is certainly a good kikashi against the corner. And
here is a useful way to follow it up, for fighting purposes, since it still threatens the corner. It is unlikely to be the correct endgame play, though, in typical situations.
Chtito: I have a question about an approaching sequence that I don't understand:
After , the sequence White a, Black b is played. Now my question is: why White does not play b instead of a? How would Black punish a white play at b?
Charles Well, if and
it becomes very dangerous for White. After
can White cut at the marked point? I don't believe so. In any case White was strong here first, so that White shouldn't have to fight in such a desperate way: it should be Black's problem to find good moves, and here it is White's.
at
is quite bad, while
at
is possible but not really interesting.