Mixed four space extension, invasion
This is often questionable, as after the cross-cut and are in good connection to the original black stones, as shown by this example sequence.
If White wants to separate the black stones, he has to enter at one of the points marked a. If White plays there, Black has to give up any hope of connecting, and should instead attack the White stone. If White instead enters at one of the b points (not often the right choice), Black can almost ensure a connection with the cross-cut.
jwaytogo: Anyone know if the attachment invasion at 'c' is a feasible move? If the four-space jump is similar to the three-space jump (see Attachment invasion of mixed three space extension), then one variation, I assume, is as follows:
My concern is that this result is probably better for black compared to the result in the 3-space invasion. I am wondering if the four-space extension could be exploited more? Note that the ladder has to be good for white.
jwaytogo: I agree with you entirely, but look at a typical end result from invading a three-space extension, where the stone at is one space to the right. Clearly this is a worse result?
Bill: I don't know what you consider typical. This may be better than that, but it still sucks.
jwaytogo: I personally find none of these results acceptable for black, unless the ladder is in black's favor. If this is the case, white would choose another variation. Black could also connect at instead of cutting at .
My question is not so much directed at the efficiency of the end-result, which is undoubtedly bad, but whether the variations for the three-space extension and four-space extension are similar, and if there are differences, what are they? I only gave this development as an example. I am assuming that one can respond to the attachment invasion of a four-space extension at any of the points labelled with a red square in the first diagram above.
Semper: That is what I would call being pulled around by the nose :).
instead of answering at 3 with 4, why not just defend directly with 4 where the white five is ? or else at a ? sure, your stones are cut, but you have a short wall on either side plus base to make territory. He'll have to choose to attack one side or the other, and either attack would be slow. It would give you time to make some other decision. Plus, you could probably easily live on either side played right ,).
My guess is that you would be scared of letting him build a small wall facing the center. while he is attack the right side, wedge out on the left and use your body. Or else stay and fight just long enough on the right side to live though you'll be helping him build an outside wall, it just depends on who you're playing and what you feel like. I wonder how you like this idea ? :)
Timm(5k): From a recent Go Game Guru commented game (Fujisawa Rina vs Mukai Chiaki, 2014 female Honimbo final). Though the actual move (for ) in the game was at a, An Younggil gives the invasion as “also possible” and proposes this sequence. The nice attachment at is played to prevent the peep at b after White's jump. (I suppose that in this case, attaching ontop of gives White too many options, but that's a good question.)
Black could look forward to this ko lock by cutting at . In this case however Black's groups will be in trouble after White lives on the side.