proposition: Lemma size_fill : forall t c, size (fill c t) >= size t.
proof: Proof. induction c. simpl. lia. simpl fill. rewrite size_fun, size_terms_cast, size_terms_app. simpl. lia. Qed.
imports: Coq(Setoid) CoLoR(LogicUtil VecUtil ListUtil BoolUtil NatUtil RelUtil)