entryIterator.remove();
    return entry;
  }

  @Override
  public SortedMultiset<E> headMultiset(@ParametricNullness E upperBound, BoundType boundType) {
    return delegate().headMultiset(upperBound, boundType);
  }

  @Override
  public SortedMultiset<E> subMultiset(
      @ParametricNullness E lowerBound,
      BoundType lowerBoundType,

  @Override
  public @Nullable Entry<E> pollLastEntry() {
    throw new UnsupportedOperationException();
  }

  @Override
  public SortedMultiset<E> headMultiset(@ParametricNullness E upperBound, BoundType boundType) {
    return Multisets.unmodifiableSortedMultiset(delegate().headMultiset(upperBound, boundType));
  }

  @Override
  public SortedMultiset<E> subMultiset(
      @ParametricNullness E lowerBound,

    entryIterator.remove();
    return entry;
  }

  @Override
  public SortedMultiset<E> headMultiset(@ParametricNullness E upperBound, BoundType boundType) {
    return delegate().headMultiset(upperBound, boundType);
  }

  @Override
  public SortedMultiset<E> subMultiset(
      @ParametricNullness E lowerBound,
      BoundType lowerBoundType,

    }

    @Override
    public @Nullable E lower(@ParametricNullness E e) {
      return getElementOrNull(multiset().headMultiset(e, OPEN).lastEntry());
    }

    @Override
    public @Nullable E floor(@ParametricNullness E e) {
      return getElementOrNull(multiset().headMultiset(e, CLOSED).lastEntry());
    }

    @Override
    public @Nullable E ceiling(@ParametricNullness E e) {

    // These are checked elsewhere, but NullPointerTester wants them checked eagerly.
    checkNotNull(fromBoundType);
    checkNotNull(toBoundType);
    return tailMultiset(fromElement, fromBoundType).headMultiset(toElement, toBoundType);
  }

  abstract Iterator<Entry<E>> descendingEntryIterator();

  Iterator<E> descendingIterator() {
    return Multisets.iteratorImpl(descendingMultiset());
  }

    assertEquals(Integer.MAX_VALUE, ms.count("b"));
    assertEquals(3, ms.count("c"));

    assertEquals(Integer.MAX_VALUE, ms.headMultiset("c", CLOSED).size());
    assertEquals(Integer.MAX_VALUE, ms.headMultiset("b", CLOSED).size());
    assertEquals(Integer.MAX_VALUE, ms.headMultiset("a", CLOSED).size());

    assertEquals(3, ms.tailMultiset("c", CLOSED).size());

    return forwardMultiset().pollLastEntry();
  }

  @Override
  public @Nullable Entry<E> pollLastEntry() {
    return forwardMultiset().pollFirstEntry();
  }

  @Override
  public SortedMultiset<E> headMultiset(E toElement, BoundType boundType) {
    return forwardMultiset().tailMultiset(toElement, boundType).descendingMultiset();
  }

  @Override
  public SortedMultiset<E> subMultiset(

                }

                if (to == Bound.INCLUSIVE) {
                  multiset = multiset.headMultiset(lastInclusive, BoundType.CLOSED);
                } else if (to == Bound.EXCLUSIVE) {
                  multiset = multiset.headMultiset(lastExclusive, BoundType.OPEN);
                }

                return multiset;
              }
            })

    // These are checked elsewhere, but NullPointerTester wants them checked eagerly.
    checkNotNull(fromBoundType);
    checkNotNull(toBoundType);
    return tailMultiset(fromElement, fromBoundType).headMultiset(toElement, toBoundType);
  }

  abstract Iterator<Entry<E>> descendingEntryIterator();

  Iterator<E> descendingIterator() {
    return Multisets.iteratorImpl(descendingMultiset());
  }

        prevEntry = null;
      }
    };
  }

  @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);
  }