4463 enclosure
This enclosure is in frequent use in contemporary go. It emphasises territory more than the 4473 enclosure does.
The prime reason for saying that is the fate of the 3-3 invasion .
The 3-3 invasion here becomes ko in this main variation; though that's not the whole story.
See http://www.gobase.org/studying/articles/matthews/ko/part5/ for commentary.
A line not covered in the above - how is White supposed to live if Black ignores the ko and plays this ?
Charles Matthews I suppose White has a choice of or a next. Black's play
seems to reduce Black's possible loss in the ko; but it also must be a concession. In practice it would be hard to kill the corner now: White must have many local ko threats such as b. Black would quite like to exchange Black c for White d, to relieve shortage of liberties around the cutting point (circled point) - but this also helps White form eyes.
There are a number of other standard invasion techniques:
- 4463 enclosure 2-4 approach
- 4463 enclosure 2-5 approach
- 4463 enclosure second-line diagonal attachment is a position that occurs both with the 2-4 and 2-5 approaches.
- 4463 enclosure 3-4 contact.
Also commonly used is the shoulderhit reduction:
Black's answer's at a and b both leave a little to be desired, so may (if well-timed) successfully prevent Black building a framework on a large scale here. Naturally, if Black intends to build in the centre, it would be more consistent to make the initial enclosure with a fourth line play (4464 enclosure, 4474 enclosure).
White may also simply play the ordinary approach move, setting up a tenuki joseki position. There are a number of ways for Black to play, depending of course on the whole framework.
This diagonal attachment has its own discussion at 4-4 point low approach low extension, tenuki.
After played as a pincer the exchange White a - Black b doesn't give White a proper base, so White is somewhat heavy here (position discussed at 4-4 point low approach low extension, slide, pincer, tenuki). Therefore White normally plays at one of the circled points.
In other circumstances the footsweep is designed to attack White's base on the outside while taking the corner.
Black may simply opt to take the corner with here.
If the direction of play is to favour the upper side, Black may also play at a or b.
Bill: Don't forget the ever popular susogakari. :-)