kb: This pattern occurs so often in my games that I want to find a good way to refute White 1 as Black in both diagrams (with and without the marked exchange in the second diagram). Does anyone know this pattern well enough to comment?
Is this where you are coming from? If so, is the gain of enough to sacrifice with moves at a and at ?
Alex: I think peeping is one option, though it's liable to start a fight.
zinger: Well, since you asked for comments, why does white play here? It looks like it could be at , in which case should probably be at a, and the fight will depend on the state of the upper left. In fact I think the state of the upper left is the key to this whole situation.
Alex: Sorry, I obviously whipped up this sequence too quickly and hallucinated... after Black b, , then W c is atari so Black has nothing here, you're right. Yes, needs to be at a, so the fight is not good for Black, especially if White is strong in the upper left as he should be if he's playing this counter-pincer strategy. The compromise diagram is probably better; I think that unless White's hypothetical position in the upper left extends along the upper side as well, the strength White gets in that direction isn't out of proportion to Black's newfound central thickness and territory on the lower side.
(As an aside, as I said in the Discussion thread, I wasn't actually asking for comments, per se, though they are of course welcome... I was just wondering aloud whether Bill and Dave's silence meant that there was nothing wrong with my suggestions, or that there was everything wrong with them ;-) )
Of course, without the slide, you can peep on the other side if you like, in which case things get even hairier. (It should be fairly easy to see why you can't peep on this side if Black has made a slide.)
Bill: Can White effectively resist with ?
Bill: I think that is a better way to connect.
Is the damage suffered by the marked stones worth the loss in the corner? Depends on the position, I'd imagine.
unkx80: Can't be at ? Then if Black plays at , then White a is atari.
Alex: Yup, same hallucination as in the other diagram. :-( I must have been tired that day.
Dave: Let's assume that the sequence begins like this, which has been seen a few times in professional play. We further assume that is played to take advantage of a White position at the top.
Dave: Most often Black plays here. It acts directly against White's desire to build up the top. If something like then strengthens the Black stones. Naturally this allows but if is sufficient for Black then not much has come of the original counter pincer.
Dave: If White plays immediately, Black could answer in the corner as above, but can also attach at to take out the left side. is painful but Black is not going to die in the corner.
Dave: Black can also exchange for before jumping to . This does not protect the corner. Instead it leaves behind a defect at a to help the two Black stones if White sets out to capture them.
The preceding diagrams all come from professional play.
Dave: I did not find any professional games where Black simply played . In any case, now comes the exchange of for followed by the attachment at . White apparantly wants to connect the stones and the attachment is a typical tesuji for doing this. Should Black want to "refute" this? here gives priority to the bottom side. This is a rather unusual follow up to the pincer, but that is another discussion :-) Playing leaves the column of Black stone in the middle outnumbered 6 to 3 after . Black should not be thinking "refutation" but rather "reasonable".
Dave: My inclination would be to play - here. This allows White to cut off 2 stones. However, those stones are not yet captured. Meanwhile Black has played on the bottom side and is pushing into White's upper left position. Remember that the basis for White's counter pincer is a White position at the top.
Bill: puts great pressure on the stones. In addition, along with the stone, it guarantees that White can connect his groups with .
What to do next depends upon the rest of the board. Dave shows how Black can make a living group, but the time may not be ripe to do that. One temptation that should probably be resisted is to run with Black's weak group. It is often better, especially early in the game, to sacrifice weak stones, even if you give up more than you should have because of earlier mistakes. Maybe the best thing to do now is nothing. Tenuki is always an option.