}

    @Override
    protected Queue<T> delegate() {
      return mmHeap;
    }

    @Override
    public @Nullable T poll() {
      return mmHeap.pollLast();
    }
  }

  public enum HeapType {
    MIN_MAX {
      @Override
      public Queue<Integer> create(Comparator<Integer> comparator) {
        return MinMaxPriorityQueue.orderedBy(comparator).create();

        NavigableSet<Integer> filtered = filter(createUnfiltered(contents), EVEN);
        NavigableSet<Integer> unfiltered = createUnfiltered(filtered);

        assertEquals(unfiltered.pollLast(), filtered.pollLast());
        assertEquals(unfiltered, filtered);
      }
    }

    public void testNavigation() {
      for (List<Integer> contents : SAMPLE_INPUTS) {

    }

    @Override
    public @Nullable E pollFirst() {
      return getElementOrNull(multiset().pollFirstEntry());
    }

    @Override
    public @Nullable E pollLast() {
      return getElementOrNull(multiset().pollLastEntry());
    }

    @Override
    public NavigableSet<E> subSet(
        @ParametricNullness E fromElement,
        boolean fromInclusive,

      return standardHigher(e);
    }

    @Override
    public @Nullable T pollFirst() {
      return standardPollFirst();
    }

    @Override
    public @Nullable T pollLast() {
      return standardPollLast();
    }

    @Override
    public SortedSet<T> headSet(T toElement) {
      return standardHeadSet(toElement);
    }

    @Override

 * defined as the <i>least</i> element in the queue according to the queue's comparator. But unlike
 * a regular priority queue, the methods {@link #peekLast}, {@link #pollLast} and {@link
 * #removeLast} are also provided, to act on the <i>greatest</i> element in the queue instead.
 *
 * <p>A min-max priority queue can be configured with a maximum size. If so, each time the size of

    public @Nullable E pollFirst() {
      synchronized (mutex) {
        return delegate().pollFirst();
      }
    }

    @Override
    public @Nullable E pollLast() {
      synchronized (mutex) {
        return delegate().pollLast();
      }
    }

    @Override
    public NavigableSet<E> subSet(
        E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) {

    public @Nullable E pollFirst() {
      synchronized (mutex) {
        return delegate().pollFirst();
      }
    }

    @Override
    public @Nullable E pollLast() {
      synchronized (mutex) {
        return delegate().pollLast();
      }
    }

    @Override
    public NavigableSet<E> subSet(
        E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) {

    public @Nullable E higher(@ParametricNullness E e) {
      return forward.lower(e);
    }

    @Override
    public @Nullable E pollFirst() {
      return forward.pollLast();
    }

    @Override
    public @Nullable E pollLast() {
      return forward.pollFirst();
    }

    @Override
    public NavigableSet<E> descendingSet() {
      return forward;
    }

    @Override

      return getSortedSetDelegate().higher(v);
    }

    @Override
    public @Nullable V pollFirst() {
      return Iterators.pollNext(iterator());
    }

    @Override
    public @Nullable V pollLast() {
      return Iterators.pollNext(descendingIterator());
    }

    private NavigableSet<V> wrap(NavigableSet<V> wrapped) {

      return map().higherKey(e);
    }

    @Override
    public @Nullable K pollFirst() {
      return keyOrNull(map().pollFirstEntry());
    }

    @Override
    public @Nullable K pollLast() {
      return keyOrNull(map().pollLastEntry());
    }

    @Override
    public NavigableSet<K> descendingSet() {
      return map().descendingKeySet();
    }

    @Override