Local Hint Resolve Permutation_app_swap_app : core.

(* Specifications: *)
Lemma Permutation_app_middle : forall l l1 l2 l3 l4,
Permutation (l1 ++ l2) (l3 ++ l4) ->
Permutation (l1 ++ l ++ l2) (l3 ++ l ++ l4).
Theorem Permutation_cons_app : forall (l l1 l2:list A) a,
Permutation l (l1 ++ l2) -> Permutation (a :: l) (l1 ++ a :: l2).