proposition: Lemma eqmx_trans m1 m2 m3 n (A : 'M_(m1, n)) (B : 'M_(m2, n)) (C : 'M_(m3, n)) : (A :=: B)%MS -> (B :=: C)%MS -> (A :=: C)%MS.
proof: Proof. by move=> eqAB eqBC; split=> [|m4 D]; rewrite !eqAB !eqBC. 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)