Mixed four space extension, invasion
Many 2d don't know about the differences between the following two shapes, but any kyu can understand it once it is explained:
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.
In this shape, and
are in no good connection to the existing black stones. White has many ways to cut conveniently, leaving one of the two black stones badly damaged.
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.
Bill: This sucks for Black. Black is very overconcentrated. If Black had the ponnuki already, would he play
? (It's even worse in the next diagram.)
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.