4-4 point low approach, two-space high pincer, without side stone
In the absence of the black stone on the side at the circled point, is joseki: a double kakari here isn't an overplay. Alternatively,
may be played at a. The high kakari at b is a variation with only a slightly different flavour. For the jump answer at c, see catenaccio joseki
Low double kakari
After the double kakari, matters can be expected to take a definite course: up to here is a very well-trodden path in joseki.
After that Black a and b are joseki continuations. Black c is no longer: this variation died a sudden death in 1992 amongst the pros.
(See also BQM362 which starts with this position asking about one of the variations given in Kogo after a).
It turns out that white here can also play this way , from move 6 there are many variations , though the most common is show here .
The variation is expected to go this way If white 6 at a , black ends up doing a squeeze against white by playing b.
To play high is also possible. Then
is still good shape. Next White at a may be the expected answer; but White directly at b has been played consistently enough in pro games since 1994.
The 3-3 invasion
If White invades the corner to get settled, up to is a common joseki. Alternatively,
can also be played at
.
Most likely, Black nows plays tenuki. There is some question about Black's play here, if Black does add a stone.
Adding is normally treated as sente by White, because Black's move next at a feels severe.
Therefore the exchange - White a is often seen here before Black takes the initiative to play in another area of the board. With the play at
, Black is trying to confine the
stone on a larger scale. Naturally,
still has plenty of aji.
It is inefficient to add both and
, though. This is Overconcentrated shape. See more at Honte / Discussion.
A compromise is for Black to play at a. This may have been invented by Kubomatsu in 1931. It gives Black a good next move here at b.