Fixpoint complete_members (env: composite_env) (m: members) : bool :=
  match m with
  | nil => true
  | (id, t) :: m' => complete_type env t && complete_members env m'
  end.

(* Specifications: *)
Lemma complete_member: forall env id t m, In (id, t) m -> complete_members env m = true -> complete_type env t = true.