Global Instance PermutationA_app :
  Proper (PermutationA ==> PermutationA ==> PermutationA) (@app A).

Lemma Permutation_eqlistA_commute l₁ l₂ l₃ : eqlistA eqA l₁ l₂ -> Permutation l₂ l₃ -> exists l₂', Permutation l₁ l₂' /\ eqlistA eqA l₂' l₃.