Let rVabelemJmx v x : x \in G -> rV_E (v *m r x) = (rV_E v) ^ x.
Fact abelem_mx_repr : mx_repr G r.
Canonical abelem_repr := MxRepresentation abelem_mx_repr.
Let rG := abelem_repr.

Lemma rV_abelem_sJ (L : {group gT}) x :
x \in G -> L \subset E -> ErV @* (L :^ x) = rowg (rowg_mx (ErV @* L) *m rG x).