proposition: Lemma mul_mxrow m n' (A : 'M[R]_(m, n')) (R_ : forall j, 'M[R]_(n', q_ j)) : A *m \mxrow_j R_ j= \mxrow_j (A *m R_ 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)