Proof. by rewrite cfDprod_cfun1l rmorph1. Qed.
Lemma cfDprod_split phi psi

(* Specifications: *)
Qed.
Proof.
rewrite inE Gxy; apply/forallP=> g. have [Gg | G'g] := boolP (g \in G); last by rewrite !cfun0 1?groupMl.
Proof.
Qed.
Definition cfBigdprodi i := cfDprodl (cfBigdprodi_subproof i) \o 'Res[
Lemma cfBigdprodi1 i (phi : 'CF(A i)) : cfBigdprodi phi 1%g = ph
- by rewrite cfRes_id.