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.