Section RowGroup.
Variable n : nat.
Local Notation rVn := 'rV[F]_n.
Definition rowg m (A : 'M[F]_(m, n)) : {set rVn} := [set u | u <= A]%MS.
Canonical rowg_group m A := Group (@rowg_group_set m A).
End RowGroup.
Variables (gT : finGroupType) (G : {group gT}) (n' : nat).
Local Notation n := n'.+1.
Variable (rG : mx_representation F G n).
Fact GL_mx_repr : mx_repr 'GL_n[F] GLval. Proof. by []. Qed.
Canonical GLrepr := MxRepresentation GL_mx_repr.
Canonical reprGL_morphism := Morphism reprGLmM.

Lemma acts_rowg (A : 'M_n) : [acts G, on rowg A | 'MR rG] = mxmodule rG A.