Section InvMorphism.
Variables (aT rT : finGroupType) (G : {group aT}) (f : {morphism G >-> rT}).
Variable R : {group rT}.
Hypothesis isoGR : isom G R f.
Definition cfQuo phi := Cfun 1 (cfQuo_subproof phi).
Local Notation "phi /  'B'" := (cfQuo phi) (at level 40) : cfun_scope.
Local Notation "phi %%  'B'" := (cfMod phi) (at level 40) : cfun_scope.
(* We specialize the cfMorph lemmas to cfMod by strengthening the domain      *)
(* condition G \subset 'N(H) to H <| G; the cfMorph lemmas can be used if the *)
(* stronger results are needed.                                               *)
(* Note that cfQuo is nondegenerate even when G does not normalize B.         *)
(* cfQuo is only linear on the class functions that have H in their kernel. *)
(* Cancellation properties *)
Definition cfDprodr := cfSdprod (dprodWsd KxH).
Definition cfDprodl := cfSdprod (dprodWsdC KxH).
Definition cfDprod phi psi := cfDprodl phi * cfDprodr psi.
Canonical cfDprodl_additive := [additive of cfDprodl].
Canonical cfDprodl_linear := [linear of cfDprodl].
Canonical cfDprodl_rmorphism := [rmorphism of cfDprodl].
Canonical cfDprodl_lrmorphism := [lrmorphism of cfDprodl].
Canonical cfDprodr_additive := [additive of cfDprodr].
Canonical cfDprodr_linear := [linear of cfDprodr].
Canonical cfDprodr_rmorphism := [rmorphism of cfDprodr].
Canonical cfDprodr_lrmorphism := [lrmorphism of cfDprodr].

Lemma cfker_dprodr psi : K \x cfker psi = cfker (cfDprodr psi).