proposition: Lemma eqmx_sym m1 m2 n (A : 'M_(m1, n)) (B : 'M_(m2, n)) : (A :=: B)%MS -> (B :=: A)%MS.
proof: Proof. by move=> eqAB; split=> [|m3 C]; rewrite !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)