proposition: Lemma rev_nztail_rev d : rev (nztail (rev d)) = nzhead d.
proof: Proof. destruct (uint_eq_dec (nztail (rev d)) Nil) as [H|H]. - rewrite H. unfold rev; simpl. rewrite <- (rev_rev d). symmetry. now apply nzhead_revapp_0. - now rewrite <- nzhead_rev, rev_rev. Qed.
imports: Decimal Arith ZArith