proposition: Corollary fmap_id_x `{FunctorLaws f} : forall (a : Type) x, fmap (@id a) x = x.
proof: Proof. intros. rewrite fmap_id. reflexivity. Qed.
imports: Hask.Ltac FunctionalExtensionality Coq.Classes.Morphisms Coq.Setoids.Setoid