}

    @Override
    public boolean removeAll(final Collection<?> collection) {
      return removeIf(collection::contains);
    }

    @Override
    public boolean retainAll(final Collection<?> collection) {
      return removeIf(element -> !collection.contains(element));
    }

    @Override

    StringBuilder sb = newStringBuilderForCollection(collection.size()).append('[');
    boolean first = true;
    for (Object o : collection) {
      if (!first) {
        sb.append(", ");
      }
      first = false;
      if (o == collection) {
        sb.append("(this Collection)");
      } else {
        sb.append(o);
      }
    }
    return sb.append(']').toString();

  /**
   * For documenting collections that support no optional features, such as {@link
   * java.util.Collections#emptySet}
   */
  NONE;

  private final Set<Feature<? super Collection>> implied;

  CollectionFeature(Feature<? super Collection>... implied) {
    this.implied = Helpers.copyToSet(implied);
  }

  @Override
  public Set<Feature<? super Collection>> getImpliedFeatures() {
    return implied;

   */
  public static boolean elementsEqual(Iterable<?> iterable1, Iterable<?> iterable2) {
    if (iterable1 instanceof Collection && iterable2 instanceof Collection) {
      Collection<?> collection1 = (Collection<?>) iterable1;
      Collection<?> collection2 = (Collection<?>) iterable2;
      if (collection1.size() != collection2.size()) {
        return false;
      }
    }

      implements TestMapGenerator<String, Collection<Integer>> {

    @Override
    public SampleElements<Entry<String, Collection<Integer>>> samples() {
      return new SampleElements<>(
          mapEntry("one", collectionOf(10000)),
          mapEntry("two", collectionOf(-2000)),
          mapEntry("three", collectionOf(300)),
          mapEntry("four", collectionOf(-40)),
          mapEntry("five", collectionOf(5)));

   * </ol>
   *
   * @param collection the presumed-immutable collection
   * @param sampleElement an element of the same type as that contained by {@code collection}.
   *     {@code collection} may or may not have {@code sampleElement} as a member.
   */
  public static <E extends @Nullable Object> void assertCollectionIsUnmodifiable(
      Collection<E> collection, E sampleElement) {
    Collection<E> siblingCollection = new ArrayList<>();

    synchronized (collection) { // for Collections.synchronized
      assertFalse(collection.spliterator().hasCharacteristics(Spliterator.NONNULL));
    }
  }

  @CollectionFeature.Require(SUPPORTS_ADD)
  public void testSpliteratorNotImmutable_CollectionAllowsAdd() {
    // If add is supported, verify that IMMUTABLE is not reported.
    synchronized (collection) { // for Collections.synchronized

      Collection<V> collection) {
    if (collection instanceof SortedSet) {
      return Collections.unmodifiableSortedSet((SortedSet<V>) collection);
    } else if (collection instanceof Set) {
      return Collections.unmodifiableSet((Set<V>) collection);
    } else if (collection instanceof List) {
      return Collections.unmodifiableList((List<V>) collection);
    }

  }

  private static <E extends @Nullable Object> Collection<E> typePreservingCollection(
      Collection<E> collection, @CheckForNull Object mutex) {
    if (collection instanceof SortedSet) {
      return sortedSet((SortedSet<E>) collection, mutex);
    }
    if (collection instanceof Set) {
      return set((Set<E>) collection, mutex);
    }
    if (collection instanceof List) {

                return super.add(element);
              }

              @Override
              public boolean addAll(Collection<? extends Integer> collection) {
                return standardAddAll(collection);
              }
            };
          }
        };

    Map<Color, Collection<Integer>> map = Maps.newEnumMap(Color.class);
    Multimap<Color, Integer> multimap = Multimaps.newMultimap(map, factory);
    try {