Instance Permutation_length' A {JA : Join A} {PA : Perm_alg A} :
  Proper (@Permutation A ==> @eq A ==> Logic.iff) joinlist | 10.

Lemma joinlist_app {A} {JA : Join A} {PA : Perm_alg A} l1 l2 x1 x2 x : joinlist l1 x1 -> joinlist l2 x2 -> join x1 x2 x -> joinlist (l1 ++ l2) x.