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.

Lemma gacent_repr (H : {set gT}) :
H \subset G -> 'C_(| 'MR rG)(H) = rowg (rfix_mx rG H).