induction lsa1; destruct lsb1; intuition.
inversion H.
inversion H.
inversion H; clear H; subst.
repeat rewrite <- app_comm_cons.
econstructor.
trivial.
eauto.
Qed.

(* Specifications: *)
Lemma list_pred_map_both :
forall (A B C D : Set)(P : A -> B -> Prop)(lsa : list A)(lsb : list B)(f1 : A -> C)(f2 : B -> D),
list_pred P lsa lsb ->
list_pred (fun c d => exists a b, P a b /\ c = (f1 a) /\ d = (f2 b)) (map f1 lsa) (map f2 lsb).