(** Permutation over lists is a equivalence relation *)

(* Specifications: *)
Theorem Permutation_refl : forall l : list A, Permutation l l.
Instance Permutation_refl' : Proper (Logic.eq ==> Permutation) id.
Theorem Permutation_sym : forall l l' : list A,
Permutation l l' -> Permutation l' l.
Theorem Permutation_trans : forall l l' l'' : list A,
Permutation l l' -> Permutation l' l'' -> Permutation l l''.