3-4 point high approach low extension
This is a Kitani joseki from the 1940s - though not exclusive to him. Black aims to make a very solid stone.
Up to is standard. In this case
leaves no weakness behind (compare with the case of
at a). This is a tight way to play.
Unusually Black can also play inside, as here. In this main line, played in 2001 in a number of pro games, Black takes a larger corner but White is thicker.
xela: On general principles (ExtensionFromAWall) wouldn't normally be at a? I found four pro games with this variation; two out of four had
at a. How would one choose?
Bill: The principle does not count the stone on the second line. The principle is based upon whether an unsupported invasion can escape or live. So the usual extension is to . (With an extension to a I think that an unsupported invasion can live in gote, at the expense of a huge thickness for White.)
For at b, see BQM186.
antic: Okay, but what if black plays like this? I played a in a game and got a very unsatisfactory result.
Bill: White would hate it if Black played atari at , so
looks like a good play. It's a double attack, threatening
and
as well as
.
Bob McGuigan: The shape in this diagram is crosscut-like and in such a situation it is always useful to ask which of your crosscut stones needs the most help. It seems the white stone on the 3-3 point needs help, so extend its liberties, as does.
Bill: Although the early play is different, in Kono Te Goyoshin (Watch out for these plays), 4-4 vol., Go Seigen shows this diagram and says that it is good for White. White aims at a or b.
Bill: It may be best to atari with first to get Black to invest a stone with
. After
something has to give.
3-4 point high approach low extension, trick play
3-4 point high approach low extension, whole board
Question on the variations resulting when black plays 5 as another hane in the last sequence: BQM186