caranthir: I think there's a problem in one of the solutions, which, if correctly resisted, leads to a ko in a small number of ways. At least I could't see a way around them, so I changed the tree accordingly.
d4rkm4tter: I agree B19-C19-E19 leads to a ko while the other two correct solutions kill. I played out the two correct solutions a bit further. That tree was small, seems I was a bit lazy in 2018 when I created this file.
up ?