proposition: Lemma mxrank_scale m n a (A : 'M_(m, n)) : \rank (a *: A) <= \rank A.
proof: Proof. by rewrite -mul_scalar_mx mxrankM_maxr. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype finfun bigop finset fingroup perm order) mathcomp(div prime binomial ssralg finalg zmodp matrix)