proposition: Lemma subst_single_eq : forall M M' P P' (MP: correct_subst M {x/P}) (MP': correct_subst M' {x/P'}), M = M' -> P = P' -> subst MP = subst MP'.
proof: Proof. intros. apply term_eq. rewrite !subst_env, H, H0; trivial. rewrite !subst_term, H, H0; trivial. Qed.
imports: CoLoR(RelExtras ListExtras TermsRed TermsConv LogicUtil) Coq(Setoid PeanoNat Lia)