Section ListDenoteProp1.
Context {A : Type}.
Variables (f : A -> Prop).
Proof with auto. rewrite listd_app, listd_unfold_and... Qed.
Proof with auto. rewrite listd_app, listd_unfold_or... Qed.
End ListDenoteProp1.
(* next - when f : A -> pred B *)

Lemma union_assoc {A} : forall (P Q R: pred A),
((P || Q) || R = P || (Q || R))%pred.