#[global]
Instance CPermutation_Equivalence A : Equivalence (@CPermutation A) | 10 := {
  Equivalence_Reflexive := @CPermutation_refl A ;
  Equivalence_Symmetric := @CPermutation_sym A ;
  Equivalence_Transitive := @CPermutation_trans A }.Implicit Types a b : A.Implicit Types l : list A.

Lemma CPermutation_app : forall l1 l2 l3, CPermutation (l1 ++ l2) l3 -> CPermutation (l2 ++ l1) l3.