Compromised diagonals and joseki 1
Without a stone at one of the marked points, this is certainly not joseki.
If White is free to extend alone the upper side, then the exchange of and
is in principle good for White. For one thing, playing
at
is joseki (3-4 point high approach outside contact).
Given a black stone at (or at the marked point), the exchange
/
is some improvement for Black: it possibly makes White heavier. Black now at a leaves White's stones floating.
White's other natural resource is at here. There is a ladder question involved. In pro games
may only be played when the ladder is good for Black: for example if White invades late and Black has some central influence.
If the ladder with is bad for White,
here is possible after
.
A second ladder (Black at a) can occur if White rejects the chance to live small here after (with
at
). This position comes from an Oteai game Yoda Norimoto-Komatsu Hideki (B) 1983-06-29.
BobMcGuigan I don't think I'd want to play in the first diagram above without some support to the right or, perhaps in a Chinese Opening type of situation, but I wondered how bad this move could be even if the ladders favor white.
For example, if things went as in the next diagram, it is clearly a bad result for Black since the marked stone is in the wrong place (it should be at a or b).
But what about this?
Andre Engels: I assume this is more or less equal, given that -
-
is a joseki, (although both a and b are clearly more common than
). The joseki is discussed in 3-4 point high approach, double contact, wall