BQM 398

19x19 diagram  

The answer is , in the largest open side area, with this possible continuation.

19x19 diagram  

This is also big, but not big enough because, according to O Meien, even if B gets the displayed sequence, ending with Ba after , W's left side and moyo is bigger than B's upper right corner and moyo.

19x19 diagram  

If B tries to get both moves in, starting with the top, the placement could happen, with B ending up with an eyeless, attackable group.

So my question (finally!) is this:

19x19 diagram  

Even after the recommended at the lower left, W could still play , threatening the same nasty placement at a. How should B counter this without looking like the third diagram and without letting W develop a position down the left side and catching in a serious pincer attack? Or should B take the pincer attack, if it comes to that, and get his compensation by playing into the 3-3 point? Remember, is supposed to be the biggest move on the board.
Thanks. --FredK

First attempt  

Jeff: My first attempt. By extending at , black simultaneously:

• Strengthens
• Attacks
• Makes the placement at a much smaller

Continuation  

If white tries the placement...

Continuation (cont.)  

Now, white has a ko for life at best (or at least to the best of my reading). And white has to make the first threat. Unfortunately. it seems a minor loss if white loses this ko, but if black loses, he's left with two weak groups. Ouch!

19x19 diagram  

Herman Hiddema: Here's an idea. With the - exchange, black defends against the placement while making white heavy. Then with , black denies white the possibility to make a base for his stones. After that, a and b are pretty much miai. If white defends the side by playing at b, black will attack the heavy - group with a. But if white connects those heavy stones by playing a himself, then black can play a double approach against the corner at b, which also attack the marked stone .

Jeff: Wow! I didn't see at all, but it does seem to solidly prevent white x. Thanks for pointing that out, Herman!

FredK: This diagram looks nice -- thanks for your thoughts. Here's a further question. Suppose W decides to tenuki after and play at 5, making a pincer. This is probably a greedy overplay, but W has some strength along the bottom so W could probably stir up trouble. How should B respond, to keep things reasonably uncomplicated? Is the potential vulnerability of the two marked W stones, after a possible B play near b, still the deciding factor?

Herman Hiddema: Well, the first thing to keep in mind, is that the - exchange doe not gain white anything locally. So if you're gonna play at , you might as well play at . That way, you can always choose what to do in the upper left corner later. Playing ther now is aji-keshi. Now on to your question. If white plays at the position of , that is a pincer of . black can then choose to jump out with a one point jump, or to take the corner with a move at 3-3. I personally would prefer to take the corner, but jumpin out also has a lot going for it (if after jump, white defends at b, you can then attack the pincer stone.

Andy Pierce: If black plays , then all black's stones on the left are low. The lower left corner is open, but white must be ok with that. Since white played the stones high, presumably for influence, it seems to me a logical continuation for white is the attachment at x. White moves at y don't look attractive since black can treat lightly as a forcing move and still undermine the lower side effectively. Just my 5 kyu guess though.