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

Lemma listd_filter h l (H : forall a b', false=h a -> g (f a) b' = b') : listd f g b (filter h l) = listd f g b l.