proposition: Lemma norm_natr x : x \is a nat_num -> `|x| = x.
proof: Proof. by move/natr_ge0/ger0_norm. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop order ssralg poly ssrnum ssrint)