Section ListDenotePred.
Context {A B : Type}.
Variables (f : A -> pred B) (b : pred B).
Proof with auto.
induction l; simpl... apply extensionality; intro x.
apply prop_ext; split; intro H. right... destruct H... inversion H.
rewrite IHl, union_assoc...
Qed.
Proof with auto.
induction l; simpl... intros [C D].
solve[rewrite listd_app; apply H; split; auto].
Qed.
Proof with simpl; try solve[exfalso; auto]; auto.
induction l... intro C; split; [ solve [apply (C a); left; auto] | ].
apply IHl...
Qed.
Proof with try solve[exfalso; auto]; auto.
revert a; induction l; simpl; intros a' C D...
destruct D as [D|D]; [rewrite <- D|].
solve [destruct C as [C1 C2]; auto]. solve[destruct C; apply IHl; auto].
Qed.

Lemma listd_In_pred_un l s :
(exists a, In a l /\ f a s) \/ b s -> listd f un b l s.