(* This code is copyrighted by its authors; it is distributed under  *)
(* the terms of the LGPL license (see LICENSE and description files) *)

(* Specifications: *)
Lemma map_in :
forall (A B : Set) (f : A -> B) (b : B) (xs : list A),
In b (map f xs) -> ex (fun a : A => b = f a /\ In a xs).