(* This provides reflexivity, symmetry and transitivity and rewriting
   on morphims to come *)

#[global]
Instance Permutation_Equivalence A : Equivalence (@Permutation A) := {
  Equivalence_Reflexive := @Permutation_refl A ;
  Equivalence_Symmetric := @Permutation_sym A ;
  Equivalence_Transitive := @Permutation_trans A }.

(* Specifications: *)
Lemma Permutation_morph_transp A : forall P : list A -> Prop, (forall a b l1 l2, P (l1 ++ a :: b :: l2) -> P (l1 ++ b :: a :: l2)) -> Proper (@Permutation A ==> Basics.impl) P.