Error: A renaming cannot be applied to a formal constraint.

What to do: Resolve feautre conflicts directly on the constraint type
  which provides the feature. This will be a class type, not a formal.
    MULTI [G -> H rename f as g end, H -> B]
  H is a formal, but you can apply the renaming to B, which is a class type:
    MULTI [G -> H, H -> B rename f as g end]