proposition: Lemma lin_mulmx_is_linear : linear lin_mulmx.
proof: Proof. move=> a A B; apply/row_matrixP=> i; rewrite linearP /= !rowE !mul_rV_lin /=. by rewrite [_ *m _](linearP (mulmxr (_ : 'M[R]__))) linearP. 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)