proposition: Lemma nf_coeff_irrelevance : forall a b n p, nf (cons a n b) -> nf (cons a p b).
proof: Proof. intros; apply nf_intro; try nf_inv. eapply nf2_intro;eauto. Qed.
imports: Arith Omega Compare_dec Relations Wellfounded Tools More_nat Wf_nat AccP not_decreasing ArithRing term rpo List