kb: I saw this in a game today on KGS. I thought it was a good strategy by Black, and I didn't quite know how to counter it. I held White. (By the way, I don't know much fuseki strategies against Sanrensei because I haven't played many people who use it effectively. Heads-up thinking on my part has usually kept their framework in check.)
What to do against ? --kb
I didn't want Black to play the All-Stars opening, so I approached the open corner.
HermanHiddema: is a bad move. It is much too slow. I don't like 3 either. I would have entered the corner at a. Then if black plays b, it is inconsistent with his earlier stones, he is blocking the wrong side. But if black plays c, his stones at ends up in a strange position. After , white could invade at d, e or f.
Bill: Earlier, I also do not like . It invites a Black play at i. The keima is better, like the proverb says. Before that, I do not like . The high approach at h contests the game plan of the yonrensei.
Charles Usually would be classed as slow: even when White has played a 4-4 point and makes a Chinese on the side, it is considered a bit relaxed. White hasn't enclosed a corner. So as an approach is more orthodox, and probably easier.
Here is something like a line commended by Fujisawa Hideyuki in a book. The idea is to fight if White now cuts.
kb: I had looked at other amateur material on Sensei's about playing against the Sanrensei - someone stating somewhere (I cannot find the page) that opposing 小目 points were good at playing against the Sanrensei.
I didn't remember the rest of the fuseki theory though. Although in hindsight I see that playing low towards the opponent's formation makes the right and left sides uninteresting so I should probably think of a more novel approach move for . Any suggestions?
Bill: is fine, here. Note its relation to .
Bill: does not work so well with on the star point. Black can continue with - , and White does not get very much on the right side. (Based on Go Seigen's commentary in 21st Century Go, as is the next diagram.)
Bill: If invades the corner, Black can expand his moyo with - , but then White's invasion with is good. (Note that is not so good when Black already has a stone at a. That's a major reason why I do not like against the yonrensei.)
kb: What about this before invading at a? If Black doesn't follow up at b, white can also extend to c.
Bill: IMO, is OK, too. Particularly since Black may well respond at or around d. But afterwards, I would generally prefer the invasion at a to the approach at c, which gives Black the opportunity to solidify his bottom side framework. Still, if you are going to play , I think it would probably be better to do so before the invasion at . It is Black's build-up of thickness in response to that invasion that makes the invasion at a urgent.