proposition: Lemma empty_presubst_neutral : forall Pt G, (forall x, In x G -> x = None) -> presubst Pt G = Pt.
proof: Proof. intro Pt; unfold presubst. sym; apply empty_presubst_neutral_aux; trivial. Qed.
imports: CoLoR(RelExtras ListPermutation TermsConv ListUtil ListExtras LogicUtil) Coq(Arith Lia)