Section Stabiliser.
Variables (m : nat) (U : 'M[R]_(m, n)).
Canonical rconj_repr := MxRepresentation rconj_mx_repr.
Local Notation rGB := rconj_repr.
Canonical quo_repr := MxRepresentation quo_mx_repr.
Local Notation rGH := quo_repr.

Lemma rstab_quo m (U : 'M_(m, n)) : rstab rGH U = (rstab rG U / H)%g.