code: public static <T> SortedSet<T> asImmutable(SortedSet<T> self) {
          return Collections.unmodifiableSortedSet(self);
      }
docs: A convenience method for creating an immutable sorted set.
  
  @param self a SortedSet
  @return an immutable SortedSet
  @see java.util.Collections#unmodifiableSortedSet(java.util.SortedSet)
  @since 1.0