David Ongaro: posetcay: You misunderstood me, I think my variation still should be considered a fail, but the same applies to all other solutions except for [current position], since an indirect Ko is much better than a direct Ko.
I.e. if B (with 'B' being the attacker here) finds a Ko thread after T16 and takes the Ko back at T17 ignores a Ko thread, he (or she) still can not resolve the Ko but has to play Q19 and the Ko continues which means B has to ignore 2 moves to win the corner.
David Ongaro: [current position] + N18Q19T16
Why is this marked incorrect, this is still a 'Black takes fist' Ko. But I think can answer my own question: Playing T4 immediately makes it and indirect Ko! (After White takes and ignores a Ko thread he still has to play Q1 and the Ko continues.) If that is the criterium (and it should be since, an indirect Ko is way superior) that also invalidates various other solutions (in particular the Atari at T4 before playing R1.)
d4rkm4tter: I tried the new feature here. I marked the branches as either ko+, ko- or dead. For now we have no way to do this automatically, but this opens possibilities to make really high quality collections with insight and learning value. Kovarex was looking at carpenter's square for this. I'd probably like to apply the 8 live 6 die corner rule. Let me know if anyone else wants to study a topic with this.
David Ongaro:
Your moves have been added.