Section ChangeOfRing.
Variables (aR rR : comUnitRingType) (f : {rmorphism aR -> rR}).
Local Notation "A ^f" := (map_mx (GRing.RMorphism.apply f) A) : ring_scope.
Variables (gT : finGroupType) (G : {group gT}).

Lemma map_regular_mx x : (regular_mx aR G x)^f = regular_mx rR G x.