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

Lemma NoDupA_equivlistA_PermutationA l₁ l₂ : NoDupA eqA l₁ -> NoDupA eqA l₂ -> equivlistA eqA l₁ l₂ -> PermutationA l₁ l₂.