RobinB: You cannot kill without a ko : the answer to the first move in the "real" solution is wrong.
If the answer is hane and not nobi, then the only way to kill is a ko.
RobinB: I proposed this problem to my Go Club and someone came with a solution that I didn't expect : white can actually obtain a ko when black plays the first good move. The sequence is a bit long so here is a sgf with it (it's AI approved).
Ivan Detkov: The real solution is to kill without ko. This is sub-optimal.
You are right. It was resolved.