Best for white. If at , then at . If at a, then black makes life with , (although he might make bigger life with ?)
Even if white has infinite ko threats, black is alive. White never gets a chance to fill a, because black can always take one of the kos, and thus threatening to make unconditional life by taking the other.
I am unsure how white counters this . a, b, c, and d are possibilities. After other moves, black makes life with d.
takes back, and after and a ko fight ensues. Black can do better than that.
takes at , at 2.
Bill: The writer was under the misapprehension that could be played at 2. The corrected sequence shows that Black dies.
fills at .
Bill: Through Black lives, but is an error.
Here is a variation I like. Black is alive in double ko.
was a real blind spot for me. I had then expected here, and Black still lives.