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

Lemma PermutationA_preserves_NoDupA l₁ l₂ : PermutationA l₁ l₂ -> NoDupA eqA l₁ -> NoDupA eqA l₂.