proposition: Lemma neutal_sn_sn M : neutral sn M -> sn M.
proof: Proof. elim. - move=> ?. by constructor=> ? /stepE. - move=> *. by apply: neutral_sn_app. Qed.
imports: Undecidability.IntersectionTypes.CD Undecidability.IntersectionTypes.Util.CD_facts Undecidability.IntersectionTypes.Util.CD_fundamental Undecidability.LambdaCalculus.Util.term_facts Relations List Wellfounded.Transitive_Closure ssreflect