Should White play a to make his group stronger or around b , which is oba?
Alex Weldon: I'd be interested to know the answer(For the record, I'd play b in a game, but I have a feeling that that's wrong... still, I'd hate to play a and give Black sente to play on the left, since he's already ahead in the balance of territory)
Charles My first thought was that a was a bit slow but ... (but I wanted to look at what the pros did). Interesting when I did: 11 examples, five at c, four at a, only two at b. So you guys have a false dichotomy here.
By the way, White's group has a well known weakness at d: but that doesn't make it a weak group in the usual sense.
Alex Weldon: Cool, thanks. I was originally going to say that c (or one line below) would have been my move, but since it wasn't given as an option, I chose b because, as you said, a seems slow, and I like to try to be fleet-footed. I'm not surprised that it's not as clear-cut as Helcio seemed to be suggesting. I don't see anything there that looks like "the only move."
unkx80: To me both a and b are playable.
BobMcGuigan: a may not be urgent for White but I think it's interesting that could be considered urgent for Black since a White move at e is big. I think I'd play a if I were playing white in this position. I'm not worried about a splitting move by Black below the starpoint on the left since White isn't going to be able to do much with a large san-ren-sei based moyo due to the strong low black stones at and .
Bill: (and, conversely, W e) is bigger than it looks, because Black has a big follow-up at d and White has a big follow-up at f. If Black had made a one space enclosure the extension to would not have been as big.
HelcioAlexandre I've been playing this position quite often lately. Most of my opponents play a (4 kyu IGS) and a few play b when I usually get's a good attack against white group later in the game. No one ever played c. My personal opinion is that a and c works well against black formation keeping it under control b ignores board position to setup a san ren sei. Playing at c would avoid a double wing formation by black that would work well with an attack against white slight weak group. Also, I don't think that a is too slow. It builds power and take away good moves that white could make against this group later in the game.
My question is:why does Go Seigen play at and not at a?
IMHO it's because of black corner enclosure on the upper right. a move at 8 does a better job in restrain black expansion on this side of the board. If white plays at a his next followup will be c. but playing at 8 he can go further at b. For black, i've read in Apreciating Famous Games that playing a e with a followup at f is the modern aproach and that playing at b is the classic way.
Also, I've seen GoSeigen playing 8 more than once against black enclosure. So I though it might be a good reason for playing this way.
Charles There is a trade-off here: one line gained on the upper side, a nerai (greater aji, as we used to say) left in the corner. It is easy to understand that there is a trade-off. I don't think we here can understand why Go Seigen plays that way.