}

  private static <E extends @Nullable Object> SortedSet<E> sortedSet(
      SortedSet<E> set, @CheckForNull Object mutex) {
    return new SynchronizedSortedSet<>(set, mutex);
  }

  static class SynchronizedSortedSet<E extends @Nullable Object> extends SynchronizedSet<E>
      implements SortedSet<E> {
    SynchronizedSortedSet(SortedSet<E> delegate, @CheckForNull Object mutex) {
      super(delegate, mutex);

  }

  private static <E extends @Nullable Object> SortedSet<E> sortedSet(
      SortedSet<E> set, @CheckForNull Object mutex) {
    return new SynchronizedSortedSet<>(set, mutex);
  }

  static class SynchronizedSortedSet<E extends @Nullable Object> extends SynchronizedSet<E>
      implements SortedSet<E> {
    SynchronizedSortedSet(SortedSet<E> delegate, @CheckForNull Object mutex) {
      super(delegate, mutex);

      implements SortedSet<E> {

    FilteredSortedSet(SortedSet<E> unfiltered, Predicate<? super E> predicate) {
      super(unfiltered, predicate);
    }

    @Override
    @CheckForNull
    public Comparator<? super E> comparator() {
      return ((SortedSet<E>) unfiltered).comparator();
    }

    @Override

    }

    @Override
    public SortedSet<V> get(@ParametricNullness K key) {
      return Collections.unmodifiableSortedSet(delegate().get(key));
    }

    @Override
    public SortedSet<V> removeAll(@CheckForNull Object key) {
      throw new UnsupportedOperationException();
    }

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