End CPermutation.
#[global]
Hint Resolve CPermutation_refl : core.
(* These hints do not reduce the size of the problem to solve and they must be used with care to avoid combinatoric explosions *)
Local Hint Resolve cperm CPermutation_sym CPermutation_trans : core.
#[global]
Instance CPermutation_Equivalence A : Equivalence (@CPermutation A) | 10 := {
Equivalence_Reflexive := @CPermutation_refl A ;
Equivalence_Symmetric := @CPermutation_sym A ;
Equivalence_Transitive := @CPermutation_trans A }.
Section CPermutation_properties.
Variable A B:Type.
Implicit Types a b : A.
Implicit Types l : list A.
(** Compatibility with others operations on lists *)

Lemma CPermutation_length_2 : forall a1 a2 b1 b2,
CPermutation [a1; a2] [b1; b2] ->
a1 = b1 /\ a2 = b2 \/ a1 = b2 /\ a2 = b1.