4-4 point low approach low extension tenuki, diagonal attachment, 3-3 invasion

Is the invasion good?  

This is a fairly fundamental position in contemporary go. The white stones on the outside may well be weak, but both players ought to be well-informed about the status of the 3-3 invasion at . Can it live?

Ordinary answer  

here must be counted as the typical answer. Alternatively, Black might block at a allowing White to connect out (nearly) at , which is purely defensive; Black might play at b which attempts to kill the corner but is bad shape; or play c, then a, which gives away eye shape to White's outside group.

Q: Can't black also answer at d?

Avoiding the overplay  

Now is usual and is probably correct shape: to play at a allows White to push through and cut, and is potentially an overplay unless Black is very strong locally^[1]. But there are still difficult tactics possible after .

Causing trouble  

White has the idea of playing at here. White could simply live now, but this sets off tactics, assuming Black plays out of fighting spirit. White cuts at .

One way to fight  

If Black plays , White will play and matters become difficult.

Another way to fight  

Black has the other option, of playing at first to see what White does. If then Black will set up the cut at b to break out. This is a tough fight.

The overplay?  

If Black does block with here, White cannot quite live in the corner. On the other hand White now has a choice of sharp ways to play.

Not quite alive, but ...  

White and aren't quite life in the corner, yet. But the cutting point at a is serious for Black. Note that White at b has a big effect in life-and-death here.

As before  

White can also play this way, a transposition into the variation considered earlier.

 

Shows up in a game of Antti Tormanen's ( http://gooften.net/2012/04/12/teaching-game-and-review-with-kamimura-haruo-9-dan/) (Note the presence of other stones in his game).

Continuation  

White can later force life at a.