proposition: Lemma mul_submxrow m n' (A : 'M[R]_(m, n')) (B : 'M[R]_(n', sq)) j : A *m submxrow B j= submxrow (A *m B) j.
proof: Proof. by apply/matrixP=> i s; rewrite !mxE; under 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)