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 rstab_in_gen m (U : 'M_(m, n)) : rstab rGA (in_gen U) = rstab rG U.