TrumpetConnectionShapeProblem/Joseki discussion

A common 4-4 joseki  

Black wants to make White overconcentrated on the right side, e.g. there might be a small white wall (too) nearby.
(Only) In that case it does not matter if White is made even stronger by the black sacrifice - and - any chance of attacking White - is lost.
Of course White might try and resist otherwise.

The continuation (1)  

Of course, White must capture the black stone . However, before doing that he still can play two useful kikashi - and - only in the right order. Kikashi is all about timing. This is an easy problem and kikashi/timing problems belong to the most difficult problems in Go.

the continuation (2)  

after the - exchange would not work, because (at ) would not be atari anymore.
The wall is now much too close to , .

The continuation (3)  

That this is not only an academic exercise is shown by the aji around a, after which White could threaten to put the stone in motion (life) or - after Black defends around b, do something else useful with the stones around a.

Charles See also attach-crosscut corner patterns. I wouldn't call the crosscut a real 'joseki': it is an example of a contextual sequence.