AdamMarquis This move is the solution to problem 30 "Expand your territory while threatening your opponent's stones" in 501 Opening Problems. This sort of move (one space approach to an enemy 2 space extension, shutting it in) is a common answer to several problems in the book. My question comes not from the validity of the move, but that I've never thought of this sort of move as threatening to White's formation. What kinds of local things could happen to White's two stones if White or Black plays here next, and how big are they? I think I've a personal problem in that I think the 2 space formation more secure than it really is.
Bill: I am pretty sure that is a good attack, here, but I do not know which one to choose.
ChrisSchack: Another possibility is to remove White's base with a here - weaken the group to chase it and make territory while doing so.
Bob McGuigan: All the attacks at and at a are good moves at the right time. In the game position it is White's move, though, and I think professionals usually respond fairly soon, usually at b or c, to strengthen the white stones and limit Black's potential.
dnerra: Hmm. First of all, I don't think are attacking moves at all. They rather strengthen white, but give black influence in return. About a: It is right that they take away eyespace, but I don't think they are a worry for White right now; White would get too much of a wall on the 3rd line in exchange for giving up the eye space.
I think a good attacking move would be Black b. It builds up Blacks moyo, and it further weakens White. Note that Black would be extremely satisfied if he got another enclosing move in sente, forcing White to make live with moves on the second line. On the other hand, it is not so easy to run out with White now: c leaves the peep at , d leaves the weakness at (the other one), and White e would strengthen Black beyond his wildest dreams.
The main point is that in the original diagram makes a lot of territory, and so all these possibilities come as a bonus, which makes it larger than any other move on the board.
Bob McGuigan: Yes, Black at b would be a strong attack, which is one reason White often responds to immediately at b. If these white stones are attacked from the outside this way, probably White will have to make defensive moves that harden the Black positions.
Shaydwyrm: I like the idea of black b also, but I would like to consider a less severe attack at f which builds a black moyo in the top right. Black then has a good follow-up at h to build his moyo, while if white ignores him, plays at a are still very strong attacks. b feels like a less useful point to occupy, since white may get to play g and reduce its value considerably, while black's followup if he plays first on the bottom (i?) seems less forceful.
Bill: - works with the stones on the bottom, building influence there.
Bill: This attack strengthens the upper right, instead.
OC, White need not respond this way to either attack.
Bill: After reading Bob's comment about White's responding to with or , I realized that I did not have to choose between strengthening the bottom or the right side, but that - would strengthen both. OC, White need not reply at , but this seems to be a good plan.
Also, judging from other responses, we seem to be heading for a consensus in favor of .
Klaus: I would play at a, which is hopefully more severe.
Timm(5k): Wouldn't b leave less aji than ? The keima attack has good follow-ups as well (see L'ame du Go). After on the other side the white's group likely to get out of trouble and may then appear to be a bit too far and high.
Dieter: As this is Black's sphere of influence, he needn't worry about aji and play solidly, but rather attack sharply and put pressure on White. You are right that a keima is an essential attacking move and it would probably be the best move if the squared stone would be alone. But here, the corner is already strong, so Black can attack with the more ambitious capping play.
Incidentally, we could also consider a keima or a capping play from the other side, towards Black solid corner. has the advantage of building a framework with Black's extension on the lower side, while a move around would build towards White extension on the upper side.
Timm: Thanks Dieter. You're saying that Black will get to build a wall around c anyway, right ? (Is White really that much in trouble ?)
Dieter: If White cuts here, Black will capture either of the cutting stones at a or b
When White cuts here, she gets into very bad shape, reducing her own liberties. If she cuts at a now, Black may counter at b and set up a common tesuji.
White is ok for now, but she cannot afford to play severely in this area. When she defends, Black can add another move to expand or solidify the sphere of influence. (I'm speaking with confidence here, but please note I'm an amateur too and can be wrong, so don't take this too authoritatively)
AdamMarquis: Answer to problem 60 "Expand your territory while attacking your opponent's weak stones." I understand the expansion of territory bit, but am confused by the stronger attacking language. Compare to the above problem "... while threatening your opponent's stones." Are the 2 White stones here weaker than the ones on the third line in the first diagram? I guess if I thought 3rd line 2 space extension formations were secure, I thought 4th line ones were super-mega-ultra secure. Again, what can happen next?
Bob McGuigan: It all depends on the surrounding position, of course, but generally the two-space extension on the fourth line may be less able to make a secure base than the one on the third line. On the other hand, the fourth line formation might be better able to run into the center. So how vulnerable a formation is depends a lot on the context.
AdamMarquis: Thanks Bob (and everyone) for comments so far. Off subject quick question: Do you remember meeting me at the Western Mass Go Club? Bad picture of me up at http://www.cookwood.com/personal/go/playerslist.html.
Bob: Sure I remember you, Adam. There's a picture of me at that site, too. I haven't been to the club for a long time, though, due to time conflicts.
dnerra: Here, Black a would be a big followup that takes away White's base and makes territory at the same time. Again, this is only a bonus to a move that is big in pure territory, too.
Bill: b is a fairly standard attack, here
minue622: For white, defence is a must, not his option. This follow-up is the most thick and solid way of defending right side's white group, so I recommend this one, especially for kyu players...
Joelr: What is the intent of the / exchange? White doesn't look heavy, and I don't see escaping. As Black, I would play in response to , and hope to come back to or one point above later.
Shaydwyrm: Alexandre Dinerchtein 1p described this or a similar position in a lecture on KGS recently. He said that is a probe, against which white can respond at or at a. If white chooses , then black defends the bottom side and white still owes another move...
Shaydwyrm: Else black will attack here, and white is in trouble. If white responds at a, apparently black can get away with not defending the bottom side because of the aji of , although the details of this I am not so sure of.
kokiri: in my kombilo database, there are 99 examples of the above formation (or with at a) with black to play, and black plays b in 30 of them, with black tenuking and white getting the next play in the rest. Of the 30 examples of black playing b, white responds to exactly none of them, and the next play in the area is usually at one of the c points. Not what my intuition tells me, certainly, but it seems to suggest that this a is not a very urgent move, and it doesn't really demand a direct response.
xela: '...this a'? Do you mean 'b'?
minue622: NEVER. In our example, black's move is THE ONLY MOVE, and necessary one, not being optional. Explanation on this would consume a lof of my time and diagrams. Sadly im busy with some silly and annoying stuffs. I will tackle on this problem at least in 30 hours, probably in 10 hours.
And the focus of this opening problem is TOO obvious, so there is no room for other choices...
Bill: While interesting, the database search is not specific enough. You really need to include at least the stone in the defence diagram. Still, I think that one lesson is clear. Shoring up the White group on the right is not urgent in the sense of urgent moves before big moves.
xela: This raises an interesting point about pro vs amateur play (not that I'm qualified to comment on this topic, but I'm going to try!) Many of the positions in 501 Opening Problems are from amateur games. In this case, the potential for black to attack white's two stones depends on the whole-board situation--b may or may not be sente, according to the context. My guess is that a pro playing white would usually not allow this formation to arise in a context where b is sente. So it's a situation which could be very common in amateur games but not show up in database searches.
minue622: " need to include at least the stone in the defence diagram...???"
What does that mean, Bill? I don't understand you.
dnerra: Don't worry, minue, Bill is agreeing with you :) He was referring to the results from pattern search. Bill's claim is that the urgency of a White defense move cannot be judge from a pattern search that just searches for the position on the right-hand side, and knows nothing about the lower side. I fully agree with that, btw. (By defence diagram he meant the diagram labelled "defence , a commom and normal follow-up.")
Bill: Thanks, dnerra, for making that clear. :-)
One thing, though. I do not like the exchange of and in the defence diagram, in part because of the stone.
Maybe White should play , which prevents that Black moyo and puts some pressure on the stone. I think that it is sufficiently light to handle a splitting attack against it and the stones.
The choice of is a light alternative to the 2-space extension. Common continuation:
- attacks. White is much thinner here than in the original problem, so it is difficult to ignore the attack. defends, the most common choice as per GoBase.
- probes; is a natural answer.
- develops the bottom. Finally, secures White's base.
White is now quite thick and ready to attack , for instance.
Dieter: I am not entirely satisfied with the answers given, because the main argument seems to be what Black can do if White doesn't answer. Now I have warned very often about plays that are only good if the opponent doesn't answer. And there is the point about equivalence, which I want to deal with first: I wonder if we all equally understand White if she were to answer at here. If Black should indeed have played in this area, then is only logical but I think that for many of us it appears to extend from a strong position and not accomplish a lot (against the corner enclosure for instance). I think we run again into Adam's problem of considering the 2 space extension stronger than it probably is.
Kirk: This may be morphing into a separate thread, but I find this notion of equivalence interesting. The white extension on the right seems pretty big to me, but I think the more important reason black plays the checking extension on the right instead of the kakari is because white has no good (big or urgent) move in the lower left. Probably the best white could do is close the corner at e3, but this has almost no effect on black. The most urgent points are sente for both sides.
Bill: Instead of , can't White extend as far as a?
Now for the other argument, the game is one where the centre is worth little. So, when exchanging - as in the next figure ...
Black extends along the side, while White jumps into the centre. To the spirit of this game, Black wins more than he loses. If White doesn't answer, we have seen in the above what can happen, but I would like the analysis to include a White move elsewhere. I do not like whole board analyses where either party passes.
Kirk: I guess that's the point of the problem -- there is no other move for white elsewhere that ameliorates the problems white now has and the benefits black has gained. Basically, the black checking extension is a good move for these very reasons. One could consider 'a' instead of 2 to reduce the growing black area in the upper right (a move near 'a' by black would probably be sente, and 'a' by white is a precursor to further reduction/invasion on the upper right side, double sente again). Black's best continuation, as discussed, is probably to build up the lower side.
Jayme: I think 1 is good because it is an extension from the shimari, because it aims at an attack which can give thickness facing two extended groups, and because any white move inside blacks spheres can be attacked in such a way to put a great deal of pressure on the two space extension. In other words it's a forcing move while taking a large point. Letting white extend on the right gives him the aim of R16 in addition, and the black extension on the bottom left of e3 does not form as large of a moyo as the right extension would. (The line height is four high as opposed to five)
AdamMarquis: This page has filled up with more information than I'd have thought possible, thank you to everyone.