package test object Test1 { class Foo[T, F[_]] def meh[M[_[_]], F[_]](x: M[F]): M[F] = x meh(new Foo[Int, List]) // solves ?M = [X[_]]Foo[Int, X[_]] ?A = List ... } object Test2 { trait TC[T] class Foo[F[_], G[_]] def meh[GG[_[_]]](g: GG[TC]) = ??? meh(new Foo[TC, TC]) // solves ?G = [X[_]]Foo[TC, X] } object Test3 { trait TC[F[_]] trait TC2[F[_]] class Foo[F[_[_]], G[_[_]]] new Foo[TC, TC2] def meh[G[_[_[_]]]](g: G[TC2]) = ??? meh(new Foo[TC, TC2]) // solves ?G = [X[_[_]]]Foo[TC, X] }