Local Notation "'Zm" := (scale_action _ _) (at level 8) : action_scope.
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.

Lemma rowg_stable m (A : 'M_(m, n)) : [acts setT, on rowg A | 'Zm].