3-4 point, 5-4 approach, one-space low pincer, separate
When white separates with 1, Black 2 and White 3 seem to be a common continuation, at which point black must choose which side to develop, possibly with a or b.
The jump down to the second line is usually slow unless White has prospects for a severe attack, for example if White occupies the two adjacent corners as in the following diagram:
moved from BQM535, there is more discussion there
Tapir: I have trouble in understanding the sequence after from onwards, any takers? Why
and not the cut, why
?
Comparison to old joseki
Uberdude: For reference here is the old version of this joseki. (In fact there are some other variations, for example can be extension at c to stop white taking the corner). Black can then continue by playing at a or b. The downside of a is that white's marked stones still has lots of aji so black isn't thick here. Sometimes white will save them immediately.
If black cuts at b he is more solid, but white can force him into a rather overconcentrated shape as shown. Note that the white stones on the outside can be treated as kikashi and sacrificed if needed.
So, now lets compare these results to the (newer) joseki in the original question. In the new joseki white's corner is a bit bigger, but black is thicker on the outside due to the extension at . This extra thickness is generally judged to be of greater benefit to black than the extra points white got in the corner (afterall white is alive in both cases).
The reason is not the cut is then it would revert to the old joseki, which is not as good for black.
takes a liberty off the black stone preparing the trade. With
he abandons the corner in order to make the cut and get sente again to extend for thickness at
, but before doing that black plays
in sente (otherwise he extends at
and white's eyes in the corner are gone).