proposition: Lemma eqmxMr m1 m2 n p (A : 'M_(m1, n)) (B : 'M_(m2, n)) (C : 'M_(n, p)) : (A :=: B)%MS -> (A *m C :=: B *m C)%MS.
proof: Proof. by move=> eqAB; apply/eqmxP; rewrite !submxMr ?eqAB. 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)