assertTrue(SortedIterables.hasSameComparator(Ordering.natural(), Sets.newTreeSet()));
    // Before JDK6 (including under GWT), the TreeMap keySet is a plain Set.
    if (Maps.newTreeMap().keySet() instanceof SortedSet) {
      assertTrue(SortedIterables.hasSameComparator(Ordering.natural(), Maps.newTreeMap().keySet()));
    }
    assertTrue(
        SortedIterables.hasSameComparator(

  }

  @LazyInit @CheckForNull private transient Set<K> keySet;

  @Override
  public Set<K> keySet() {
    Set<K> result = keySet;
    return (result == null) ? keySet = new KeySet() : result;
  }

  @WeakOuter
  private class KeySet extends ForwardingSet<K> {
    @Override
    protected Set<K> delegate() {
      return delegate.keySet();
    }

    @Override
    public void clear() {

                    }
                    return multimap.keySet();
                  }

                  @Override
                  public List<String> order(List<String> insertionOrder) {
                    return Ordering.natural().nullsFirst().sortedCopy(insertionOrder);
                  }
                })
            .named("TreeMultimap.keySet")
            .withFeatures(

    assertTrue(multimap.keySet() instanceof SortedSet);
    assertTrue(multimap.asMap() instanceof SortedMap);
  }

  public void testTreeKeys_gwtCompatible() {
    ListMultimap<String, Integer> multimap =
        rawtypeToWildcard(MultimapBuilder.treeKeys()).arrayListValues().<String, Integer>build();
    assertTrue(multimap.keySet() instanceof SortedSet);

    }
  }

  public void testAsMapGetImplementsList() {
    for (K key : multimap().keySet()) {
      assertTrue(multimap().asMap().get(key) instanceof List);
    }
  }

  @MapFeature.Require(SUPPORTS_REMOVE)
  public void testAsMapRemoveImplementsList() {
    List<K> keys = new ArrayList<>(multimap().keySet());
    for (K key : keys) {
      resetCollection();

    getMap().remove(k0());
    expectMissing(e0());
  }

  @MapFeature.Require(SUPPORTS_REMOVE)
  @CollectionSize.Require(absent = ZERO)
  public void testRemoveKeyFromKeySetRemovesFromInverse() {
    getMap().keySet().remove(k0());
    expectMissing(e0());
  }

  @MapFeature.Require(SUPPORTS_REMOVE)
  @CollectionSize.Require(absent = ZERO)
  public void testRemoveFromValuesRemovesFromInverse() {

    assertThat(multimap.keySet()).containsExactly("foo", "bar", "cow").inOrder();
    assertThat(multimap.removeAll("foo")).containsExactly(6, 7).inOrder();
    assertThat(multimap.keySet()).containsExactly("bar", "cow").inOrder();
    assertTrue(multimap.remove("bar", 4));
    assertThat(multimap.keySet()).containsExactly("bar", "cow").inOrder();
    assertTrue(multimap.remove("bar", 1));

    // Tests that serializing a map, its keySet, and values only writes the underlying data once.

    Entry<Integer, Integer>[] entries = (Entry<Integer, Integer>[]) new Entry<?, ?>[1000];
    for (int i = 0; i < 1000; i++) {
      entries[i] = ImmutableMap.entryOf(i, i);
    }

    ImmutableMap<Integer, Integer> map = RegularImmutableMap.fromEntries(entries);
    Set<Integer> keySet = map.keySet();

      expectedModCount = modCount;
      toRemove = null;
    }

    abstract T output(BiEntry<K, V> entry);
  }

  @Override
  public Set<K> keySet() {
    return new KeySet();
  }

  private final class KeySet extends Maps.KeySet<K, V> {
    KeySet() {
      super(HashBiMap.this);
    }

    @Override
    public Iterator<K> iterator() {
      return new Itr<K>() {
        @Override

    }
  }

  abstract Iterator<Entry<K, V>> entryIterator();

  @LazyInit @CheckForNull private transient Set<K> keySet;

  @Override
  public Set<K> keySet() {
    Set<K> result = keySet;
    return (result == null) ? keySet = createKeySet() : result;
  }

  abstract Set<K> createKeySet();

  @LazyInit @CheckForNull private transient Multiset<K> keys;

  @Override