FilteredSet<E> filtered = (FilteredSet<E>) unfiltered;
      Predicate<E> combinedPredicate = Predicates.and(filtered.predicate, predicate);
      return new FilteredSortedSet<>((SortedSet<E>) filtered.unfiltered, combinedPredicate);
    }

    return new FilteredSortedSet<>(checkNotNull(unfiltered), checkNotNull(predicate));
  }

  /**