docs: public static <T> Reducer<PersistentSortedSet<T>,T> toPersistentSortedSet() {
          return Reducer.fromMonoid(Monoids.concatPersistentCollection(TreeSet.empty(Comparators.naturalOrderIdentityComparator())),
                  a -> TreeSet.of(Comparators.naturalOrderIdentityComparator(),a));
  
      }