you'd have to declare your interfaces like this :

interface Wtf<out A, out B, out C : Ftw<A, B>>
interface Ftw<out A, out B>

Thanks, you've saved my evening! Thought it's impossible.

No problem, be careful though as this might open up the portal to generics hell 😉

Yea, thanks. I've read it, my generics are just too complicated, getting analysis paralysis sometimes 🙂