proposition: Lemma nf_inv1 : forall a n b, nf (cons a n b) -> nf a.
proof: Proof. unfold nf; destruct b; cbn. - auto. - destruct (nf_b a); auto. Qed.
imports: Coq(Arith Max Bool Lia Compare_dec Relations Ensembles Wellfounded Bool RelationClasses Operators_Properties ArithRing Logic.Eqdep_dec) hydras(More_Arith Restriction DecPreOrder) hydras(OrdNotations)