Hi, in this situation, if White fails to play 4, what happens when Black plays there? White doesn’t play inside, Black fills the last outside liberty, White doesn’t play inside again, Black makes a Bent-four in the corner and have to win the ko? So White gave a chance for Black to win with just 1 ko fight instead of 2, is this reasoning correct? Thanks.
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black can remove all possible ko threats 1st on entire board and only then start bent 4 ko fight, then black would inevitably win it and white will be dead.
So if there is no unremovable ko threat on the board, bent 4 is just dead, no need to actually remove all ko threats and to start bent 4 battle.
If it’s possible to place black stone on Q1, white is dead.
If white tries to escape by playing Q1 and fails, white is dead.
Oh thanks, I fell for the “bent four in the corner” semantics trap again … the difference between the eye shape itself and the shapes that lead to it.
Since I’m still on the rectangle in the corner with one outside liberty, why the sources I see only mention one vital point for the defense (the one near the border)? Aren’t both points valid or am I missing something? That seems even better than playing at 2, since there are no more ko threats that Black can make.
Is your question whether white S2 is a better defense than white T2?
Thinking about ko threats is the right idea, but it looks like S2 leaves one ko threat (as you show in your diagram) while T2 leaves no ko threats!
Yes, thanks, that was the question, but what is the ko threat here? White is already safe with 2 eyes. With T2 there’s “4”:
In your first diagram, white cannot safely ignore this black move:
So black T2 is the ko threat here.
In your second diagram:
White can in fact safely ignore black S2 (thanks to the outside liberty at Q1).
So black has zero ko threats after white defends at T2.
Ah ok, I was calling ko threats, the moves after the first one, so changing my terminology I meant the first diagram you posted has 1 ko threat and the second has 2. I guess we agree on the first one. And in the second one I see your correction now: White can tenuki once, because something like this is the worst that can happen and only then White acts:
I think we’re on the same page, my brain hurts 
I’m trying to understand everything about the rectangles. Next stop → L on the corner.