From Gokyo Shumyo, Section 1, Problem 70. I can't find the refutation for , but it is late too. --Dieter
Let us consider this to be the basic variation (involving no ko). We will reconsider and . and are miai. is clearly wrong: takes the vital point. If now Black a, White has enough outside liberties to capture Black's bent four. If Black doesn't play a, White a makes seki.
But here is better: a and b are miai: Black a - White b is symmetrical to the first diagram and Black b - White a gives White the time to capture the three stones and make two eyes.
assures ko. At the moment I am not able to tell if it will become double ko (which means life) or not. This surely means I don't understand ko.
(Sigh) Let's suppose it is some sort of ko, still worse than unconditional life. Then we must proceed to an alternative for in "Attempt 1".
Since was the correct move in Gokyo Shumyo, Section 1, Problem 70 / Solution, chances are that it saves the day again. Given Gokyo Shumyo, Section 1, Problem 70 / Solution, is not the answer, but obviously White at will make two eyes.
We're back to where we started. The hane is not the solution, because it enables White to grab the vital point again. So, let's have Black play there himself.