proposition: Lemma normr_nneg (R : numDomainType) (x : R) : `|x| \is Num.nneg.
proof: Proof. by rewrite qualifE/=. Qed.
imports: mathcomp(all_ssreflect ssralg ssrint ssrnum matrix) mathcomp(interval rat) mathcomp(boolp classical_sets functions) mathcomp(mathcomp_extra) reals ereal signed topology normedtype landau sequences derive realfun itv convex