trait HomClass { self =>
  type L
  type H>:L
  type C[_>:L<:H,_>:L<:H]
  type Dual <: HomClass {
    type L=self.type#L
    type H=self.type#H
    type C[A>:L<:H,B>:L<:H] = self.type#C[B,A]
    type Dual = self.type
  }
}
object foo extends HomClass { type L = Nothing; type H = Nothing; type C[A,B] = Int => Double }