code: protected SortedMultiset<E> standardSubMultiset(
        E lowerBound, BoundType lowerBoundType, E upperBound, BoundType upperBoundType) {
      return tailMultiset(lowerBound, lowerBoundType).headMultiset(upperBound, upperBoundType);
    }
docs: A sensible definition of {@link #subMultiset(Object, BoundType, Object, BoundType)} in terms of
  {@link #headMultiset(Object, BoundType) headMultiset} and {@link #tailMultiset(Object,
  BoundType) tailMultiset}.
  
  <p>If you override either of these methods, you may wish to override {@link
  #subMultiset(Object, BoundType, Object, BoundType)} to forward to this implementation.