Fixpoint list_denote l : T :=
  match l with nil => b | x :: l' => g (f x) (list_denote l')
  end.Notation "'un'" := (@orp _).

Lemma listd_flat_map h l (H : forall a b', g (f a) b' = listd f g b' (h a)) : listd f g b l = listd f g b (flat_map h l).