removeIfEmpty();
      }
      return changed;
    }

    @Override
    public boolean removeAll(Collection<?> c) {
      if (c.isEmpty()) {
        return false;
      }
      int oldSize = size(); // calls refreshIfEmpty
      boolean changed = delegate.removeAll(c);
      if (changed) {
        int newSize = delegate.size();
        totalSize += newSize - oldSize;

    testers.add(SetEqualsTester.class);
    testers.add(SetRemoveTester.class);
    // SetRemoveAllTester doesn't exist because, Sets not permitting
    // duplicate elements, there are no tests for Set.removeAll() that aren't
    // covered by CollectionRemoveAllTester.
    return testers;
  }

  @Override
  protected List<TestSuite> createDerivedSuites(

  public boolean remove(@Nullable Object key, @Nullable Object value) {
    return delegate().remove(key, value);
  }

  @CanIgnoreReturnValue
  @Override
  public Collection<V> removeAll(@Nullable Object key) {
    return delegate().removeAll(key);
  }

  @CanIgnoreReturnValue
  @Override
  public Collection<V> replaceValues(@ParametricNullness K key, Iterable<? extends V> values) {

  }

  @Override
  public int hashCode() {
    return delegate().hashCode();
  }

  /**
   * A sensible definition of {@link #removeAll} in terms of {@link #iterator} and {@link #remove}.
   * If you override {@code iterator} or {@code remove}, you may wish to override {@link #removeAll}
   * to forward to this implementation.
   *
   * @since 7.0 (this version overrides the {@code ForwardingCollection} version as of 12.0)
   */

  public boolean remove(@Nullable Object key, @Nullable Object value) {
    return delegate().remove(key, value);
  }

  @CanIgnoreReturnValue
  @Override
  public Collection<V> removeAll(@Nullable Object key) {
    return delegate().removeAll(key);
  }

  @CanIgnoreReturnValue
  @Override
  public Collection<V> replaceValues(@ParametricNullness K key, Iterable<? extends V> values) {

  @Override
  public boolean remove(@Nullable Object o) {
    assertTrue(Thread.holdsLock(mutex));
    return super.remove(o);
  }

  @Override
  public boolean removeAll(Collection<?> c) {
    assertTrue(Thread.holdsLock(mutex));
    return super.removeAll(c);
  }

  @Override
  public boolean retainAll(Collection<?> c) {
    assertTrue(Thread.holdsLock(mutex));
    return super.retainAll(c);
  }

  @Override
  public boolean remove(@Nullable Object o) {
    assertTrue(Thread.holdsLock(mutex));
    return super.remove(o);
  }

  @Override
  public boolean removeAll(Collection<?> c) {
    assertTrue(Thread.holdsLock(mutex));
    return super.removeAll(c);
  }

  @Override
  public boolean retainAll(Collection<?> c) {
    assertTrue(Thread.holdsLock(mutex));
    return super.retainAll(c);
  }

@GwtCompatible
public final class Sets {
  private Sets() {}

  /**
   * {@link AbstractSet} substitute without the potentially-quadratic {@code removeAll}
   * implementation.
   */
  abstract static class ImprovedAbstractSet<E extends @Nullable Object> extends AbstractSet<E> {
    @Override
    public boolean removeAll(Collection<?> c) {
      return removeAllImpl(this, c);
    }

    @Override
    public boolean retainAll(Collection<?> c) {

   *
   * <p>This is essentially the same as {@code
   * TreeRangeSet.create(this).removeAll(other.complement())} except it returns an {@code
   * ImmutableRangeSet}.
   *
   * @since 21.0
   */
  public ImmutableRangeSet<C> intersection(RangeSet<C> other) {
    RangeSet<C> copy = TreeRangeSet.create(this);
    copy.removeAll(other.complement());
    return copyOf(copy);
  }

  /**

  }

  @Override
  public final boolean addAll(Collection<? extends E> newElements) {
    throw new UnsupportedOperationException();
  }

  @Override
  public final boolean removeAll(Collection<?> oldElements) {
    throw new UnsupportedOperationException();
  }

  @Override
  public final boolean removeIf(Predicate<? super E> predicate) {
    throw new UnsupportedOperationException();
  }