Compromised diagonals and joseki 1

Not joseki  

Without a stone at one of the marked points, this is certainly not joseki.

White's shape is better  

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).

Chinese formation case  

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.

Ladder question  

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.

The ladder in question  

If the ladder with is bad for White, here is possible after .

A second ladder  

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.

Charles Matthews

Bad for Black  

But what about this?

More or less equal?  

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