...in which black concedes running room to white while taking sure but modest territory. The reducing stones are always a concern for white, and he usually spends a move to connect them to something midway through the game.
The solidly aggressive extension is sometimes played:
...in which black concedes both some eastward running room to white, and some westward invasion, in return for a solid position. Black always takes 'a' and usually something around 'b'.
But the upper hane is notable in that it blocks both an immediate run eastward, and any play underneath. The former is obvious. The latter looks like this:
The important thing for me is to be able to suppress the moyo and not have to come back an d protect 'a' in certain gote. To that extent, both of the previous diagrams work for me. Whether I end in gote or not is not clear, as getting to the corner is big.
I feel like he would have done some of that light dodgy business if I gave him more space to. He might, still, but it seems harder on the board this way. This is kind of hard to respond to (the best I seem to have is 'a', because against many moves, black can just sacrifice one stone and jump out with the other for a successful reduction.
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The only question in my mind, really, was whether 24 should be above or below the two stones. If this is safe, this seems best, as it doesn't grant the atari and the aji that comes with. As I can't seem to read anything too bad, I'm going with this. White could play more aggressively to break into my left side, by forcing me to capture 23, but his resulting stones will all be weak and potentially heavy. I feel like I can be content with this unless I'm missing something huge.
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To observers: ( BTW, there is lots of good stuff for beginners in here)
To put things in perspective: remember that a few moves back I was faced with a burgeoning black left side, and a my own thinness up top. To remedy both of those problems simultaneously, I threatened to invade the left, assuming that I could either get an invasion or an outside wall. MHO made the most aggressive possible reply, denying any chance of an invasion, so I'm going for the wall. Its approximate future location is indicated by the triangles. Not only does a wall hold him back on the left, but I don't have to make small gote moves up top, for once the wall is in place, the two circled stones are no longer thin, but function as extensions off of the wall.
So the issue for me is how to construct that wall.
Note to beginners:
As a general rule, a wall is considered to be worth about 2.5 to 3 points per stone. This value varies widely depending upon circumstances. So if I sacrifice a stone, or even two, and my wall gets one stone longer as a result, it is a net profit for me. The general idea is that the three stones will die, but the the black stones surrounding them are not themselves clearly alive yet, and they can be threatened by white stones crowding them from the east. That means that in some instances the play of those crowding stones will be atari, and therefore sente.
The immediate threat, of course is the double atari at 'a', and the escape at 'b'. Not surprisingly, those are his two best options.
Note to beginners:
There is a proverb that "The opponent's best play is my best play". Sometimes, an easy way to cause trouble for your opponent is to figure out where he would want to play, and then play there yourself.
White 4 starts to assemble the pieces of wall, and is more aggresive than it looks. Because of the aji of the three sacrifice stones, taking the corner is big:
As mentioned above, the idea of the sacrifice is to threaten the surrounding stones, and gain while doing so. The prior three diagrams illustrate this. White builds a wall and takes territory, while black is backpedaling. The three sacrifice stones threaten to assist in the kill.
My current guess at black's best(?) result is this:
Observe how the three doomed stones still play a role. The surrounding black stones repeatedly find themselves in danger, partly due to the threat of the 'dead' stones. Also, note the clumpy shpe of the black stones.
How consistent is the 2.5-3 pts per stone rule? I had heard that, but I assumed it applied to walls on the 3rd or 4th line. A wall on the 6th line must be worth less, right?
I'm also curious as to how you would work things like extensions into that. Presumably a wall that already has a good extension, or that completes a moyo, is worth more, but do you have any sense of how much more?
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Unfortunately, both players do not realize the problem started with the atari. In fact, much of the analysis in Post #88 shows the issues stemming from it. IMO, the evaluation of the situation should start with this sequence instead (and it'd be nice for beginners to be aware of the differences between the two ataris) --
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Caveat: this post contains some wild-ass guesses.
jts wrote:
How consistent is the 2.5-3 pts per stone rule? I had heard that, but I assumed it applied to walls on the 3rd or 4th line. A wall on the 6th line must be worth less, right?
Not a whole lot less. The effect of a wall falls off as some function of the inverse of the distance. ( I suspect that the function is one term and something between x^1 and X^2 ) In this case it is like having a wall on the fourth rank and having someone chop off rows 's' and 't'. Or maybe a better way to consider it is a fourth-rank wall with a few stones on the opposite side of the board, which would locally neutralize the effect of the wall 11 or 12 stones away.
How much is the difference in value ( to the east ) of this wall:
Presumably, whatever effect the wall might have on the two most eastern rows is zero, as it is neutralized by the white stones there. But, in practice, would you consider the wall worth sustantially less?
What then, is the difference between the wall above and the one below?
I'm also curious as to how you would work things like extensions into that. Presumably a wall that already has a good extension, or that completes a moyo, is worth more, but do you have any sense of how much more?
Well, since it takes 2 moves to play those stones, and the current temperature is maybe 10 *shrug*, then it might follow that the stones - if perfectly placed - would raise the value of the wall about 20 points. But they are not perfectly placed. The one at J17 is too close to the wall and too far away from its neighbor. It should be at L16 or L17, I think. That imperfection is hard to evaluate.
I do not see why he needs the marked stone exchange. The exchange seems to add to the number of stones sacrificed, while allowing black to fix that local area. I'm not sure what good it does for white. If he wants to go that route, I'd think it'd be better to skip the exchange, and just play what he wanted to:
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I'm not entirely convinced by his reasoning either, although I think the result is close to the same. However, I think this is a really poor overall final result on the left for White:
Sure, it requires , but is so huge that I can't see it being omitted, and it's fairly obviously urgent after . It's a really really huge corner and side.
This doesn't seem too bad. I'm capturing some stomnes and making fourth-line territory. It seems likely that Joaz is going to use forcing moves against my stones here to take a bit of thickness here, but I think that's doable. E14 looks unlikely to link solidly in sente, so his thickness will either be flawed or gote, in which case I can start reducing. If I reduce, I'll have to consider either capping one of the low middle under-the-star-point stones on the top and bottom, or just leaning on his framework from the right side.
I am also a little concerned that he could steal my corner here. While he could do so in gote with a fairly safe joseki, he could also do something aggressive like this. My concern here is the number of liberties I have on the D14 group. This is enough of a concern that I may play to protect the corner soon, if he doesn't get there first. Or at least threaten F17, so he cannot take the corner without sacrificing that area.
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I can see that playing inside first gives b an empty triangle, but it also absolutely ensures that black encloses the territory, which is what confuses me. In other words, though black has an empty triangle, I feel the benefit of solidly walling off territory seems greater than white's benefit.
How does white benefit from an exchange leading to an empty triangle if the empty triangle is part of a now solidly connected wall?
If the exchange had not been made, isn't there the small possibility of a ko threat in the area, which has now been extinguished?
Annoyingly, it feels like I need to spend a move in the corner to button it up, removing aji. This gets me some points, but at this stage of the game it feels slow. However, I really don't like the idea of my opponent getting the corner invasion in sente because of threats against D16. So I'll play the slow defensive move that looks like it works (shown above), and hope to be able to reduce my opponent sufficiently after that. At least I should have a big chunk of points on the left. I feel like my handicap is reduced, but not entirely gone.
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EdLee
White has several options:
atari is OK, but the other way (B atari at 
instead) is still better:
and 
here: 
, but 
. It's a really really huge corner and side.
first, then later if W turns at (a),
Bwaahahahaha...