proposition: Lemma addsmxSr : (B <= A + B)%MS.
proof: Proof. by have:= submx_refl (A + B)%MS; rewrite addsmx_sub; case/andP. 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)