}
  }

  @Override
  public Iterator<E> iterator() {
    return Multisets.iteratorImpl(this);
  }

  @Override
  public SortedMultiset<E> headMultiset(@ParametricNullness E upperBound, BoundType boundType) {
    return new TreeMultiset<>(
        rootReference,
        range.intersect(GeneralRange.upTo(comparator(), upperBound, boundType)),
        header);
  }