Proof. by split; [apply: map_mxM | apply: map_mx1]. Qed.

(* Specifications: *)
Lemma map_lin1_mx m n (g : 'rV_m -> 'rV_n) gf :
Lemma map_lin_mx m1 n1 m2 n2 (g : 'M_(m1, n1) -> 'M_(m2, n2