Local Hint Resolve Permutation_cons_app : core.

(* Specifications: *)
Lemma Permutation_Add a l l' : Add a l l' -> Permutation (a::l) l'.
Theorem Permutation_middle : forall (l1 l2:list A) a,
Permutation (a :: l1 ++ l2) (l1 ++ a :: l2).