Endgame Tesuji 11

Tesuji  

is the tesuji.

Result: 10 pts. for Black in the corner  

It allows White to get both hanes in sente.

Mistake 1: 12 pts. for Black  

Now, the hane at a is gote.

Mistake 2: 12 pts. for Black  

Now, the hane at a is gote.

A slight gain for white?  

Perhaps white can still gain something like this. But it is nowhere near as good as getting both hanes in sente. Black has only one less point than in the failure diagrams, and can play a later to maybe make up that point in ko.

Another variation: 9 pts. for Black  

This way a is likely sente for black, offsetting the corner loss. So perhaps this tesuji requires white to have a stone on the top so that a is gote?

--- If a is really double sente, then there are a number of complication - for one thing, black can probably sacrifice part of the group for mutual damage. Can we add another problem to clarify what the tesuji is supposed to be? "Play a forcing move at the point that protects both hanes"? If that's the idea then we can just change the problem to make :b2: at the 3-3 urgent.

--- tapir: I agree, we should clarify this. This is now more a puzzle / problem than the clear tesuji we tried to present.

--- Bill: a is not double sente, but unclear edges of endgame problems can cause trouble. I have added a White stone to the first diagram to clarify things.