EdIV: I was looking at the result of this descend [current position]. Because looking at the current variations it should be the only correct move. (White lives without ko). But I found a way for Black to kill after White's descend. I'll add an SGF.
fieramosca: [current position] According to my book, the opponent can force a ko from this position with A17G18C18C19B18F17A19
Ivan Detkov: It is interesting. I added this variant and marked the ko as the right solution. I did not remove the existing variants. If somebody thinks it should be improved - go ahead.
Should it be B1 jump instead?