proposition: Lemma eqmx_conform m1 m2 n (A : 'M_(m1, n)) (B : 'M_(m2, n)) : (conform_mx A B :=: A \/ conform_mx A B :=: B)%MS.
proof: Proof. case: (eqVneq m2 m1) => [-> | neqm12] in B *. by right; rewrite conform_mx_id. by left; rewrite nonconform_mx ?neqm12. 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)