proposition: Lemma mxsub_mul m n m' n' p f g (A : 'M_(m, p)) (B : 'M_(p, n)) : mxsub f g (A *m B) = rowsub f A *m colsub g B :> 'M_(m', n').
proof: Proof. by split_mxE; under [RHS]eq_bigr do rewrite !mxE. 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 countalg finalg zmodp)