@Override
    public boolean removeAll(Collection<?> c) {
      return removeAllImpl(this, c);
    }

    @Override
    public boolean retainAll(Collection<?> c) {
      return super.retainAll(checkNotNull(c)); // GWT compatibility
    }
  }

  /**
   * Returns an immutable set instance containing the given enum elements. Internally, the returned

    @Override
    public boolean removeAll(Collection<?> c) {
      return removeAllImpl(this, c);
    }

    @Override
    public boolean retainAll(Collection<?> c) {
      return super.retainAll(checkNotNull(c)); // GWT compatibility
    }
  }

  /**
   * Returns an immutable set instance containing the given enum elements. Internally, the returned

      synchronized (mutex) {
        return delegate().removeAll(c);
      }
    }

    @Override
    public boolean retainAll(Collection<?> c) {
      synchronized (mutex) {
        return delegate().retainAll(c);
      }
    }

    @Override
    public int size() {
      synchronized (mutex) {
        return delegate().size();
      }
    }

                  }

                  @Override
                  public boolean retainAll(Collection<?> c) {
                    return Iterators.retainAll(iterator(), c);
                  }
                };
              }
            })
        .named("ArrayList with Iterators.removeAll and retainAll")
        .withFeatures(

      synchronized (mutex) {
        return delegate().removeAll(c);
      }
    }

    @Override
    public boolean retainAll(Collection<?> c) {
      synchronized (mutex) {
        return delegate().retainAll(c);
      }
    }

    @Override
    public boolean removeIf(Predicate<? super E> filter) {
      synchronized (mutex) {

                  }

                  @Override
                  public boolean retainAll(Collection<?> c) {
                    return Iterators.retainAll(iterator(), c);
                  }
                };
              }
            })
        .named("ArrayList with Iterators.removeAll and retainAll")
        .withFeatures(

   * @param elementsToRetain the elements to retain
   * @return {@code true} if any element was removed from {@code iterator}
   */
  @CanIgnoreReturnValue
  public static boolean retainAll(Iterator<?> removeFrom, Collection<?> elementsToRetain) {
    checkNotNull(elementsToRetain);
    boolean result = false;
    while (removeFrom.hasNext()) {
      if (!elementsToRetain.contains(removeFrom.next())) {

   * @param elementsToRetain the elements to retain
   * @return {@code true} if any element was removed from {@code iterator}
   */
  @CanIgnoreReturnValue
  public static boolean retainAll(Iterator<?> removeFrom, Collection<?> elementsToRetain) {
    checkNotNull(elementsToRetain);
    boolean result = false;
    while (removeFrom.hasNext()) {
      if (!elementsToRetain.contains(removeFrom.next())) {

    assertThrows(UnsupportedOperationException.class, () -> values.removeAll(singleton("four")));
    assertThrows(UnsupportedOperationException.class, () -> values.retainAll(singleton("four")));
    assertThrows(
        UnsupportedOperationException.class,
        () -> {
          Iterator<String> iterator = values.iterator();
          iterator.next();