Definition rowval_gen m U :=
<<\matrix_ik
mxvec (\matrix_(i < m, k < d) (row i (val_gen U) *m A ^+ k)) 0 ik>>%MS.

Lemma rstabs_in_gen m (U : 'M_(m, n)) :
rstabs rG U \subset rstabs rGA (in_gen U).