code: public static <E, S extends SortedSet<E>> MutableSortedSet<E> of(S set, Object lock)
      {
          return new SynchronizedSortedSet<E>(SortedSetAdapter.adapt(set), lock);
      }
docs: This method will take a MutableSortedSet and wrap it directly in a SynchronizedSortedSet.  It will
  take any other non-GS-collection and first adapt it will a SortedSetAdapter, and then return a
  SynchronizedSortedSet that wraps the adapter.  Additionally, a developer specifies which lock to use
  with the collection.