TherapieGo: In Black to play. I've just spent the whole afternoon researching this crazy problem... My conclusion is that the best solution for Black and White is a Ko that White takes first, Black can't get any better. Here's the sequence, [current position] + E18C18A18A17B17A19A16E19D19F19A18C19B19 I'm also posting my SGF with all the interesting sequences, I've put 3 possible resistances for White so you can watch what happens in each of them. I don't know if anyone will be motivated to take over this entire file, but good luck to whoever does!
TherapieGo: In Black to play. First of all : [current position] + A15C18A17 Impossible to kill unconditionally. The problem with this Tsumego when I tried to use Katago to discover the truth of this problem (as usual ^^) I realized that if I create a situation in which black can win all the Ko then I discover many different Ko sequences depending on how White responds and so it's very difficult to know which sequences are the most interesting. In contrast, if I create a situation in which White can win all the Ko then it could be that White's best answer is A18 when Black starts with B18 and the sequence could be B18A18A17C18E18B19A19, but it's extremely difficult to determine whether this is the best way...
You are right. S3 is not working and T7 taking 2 stones is not working either. Should it be an alternative solution?