}

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

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

  }

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

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

      implements SortedSet<E> {

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

    @Override
    public @Nullable 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(@Nullable Object key) {
      throw new UnsupportedOperationException();
    }

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

  }

  private static class NonNavigableSortedSet extends ForwardingSortedSet<String> {
    private final SortedSet<String> delegate = Sets.newTreeSet();

    @Override
    protected SortedSet<String> delegate() {
      return delegate;
    }
  }

  public void testAsMapSorted() {
    SortedSet<String> strings = new NonNavigableSortedSet();
    Collections.addAll(strings, "one", "two", "three");

     * @param s the sorted set to be placed in the created set
     * @return a new instance of {@link ConcurrentSkipListSet}
     * @see ConcurrentSkipListSet#ConcurrentSkipListSet(SortedSet)
     */
    public static <E> ConcurrentSkipListSet<E> newConcurrentSkipListSet(final SortedSet<? extends E> s) {
        return new ConcurrentSkipListSet<E>(s);
    }

    /**
     * Creates and returns a new instance of {@link CopyOnWriteArrayList}.

  }

  private static class NonNavigableSortedSet extends ForwardingSortedSet<String> {
    private final SortedSet<String> delegate = Sets.newTreeSet();

    @Override
    protected SortedSet<String> delegate() {
      return delegate;
    }
  }

  public void testAsMapSorted() {
    SortedSet<String> strings = new NonNavigableSortedSet();
    Collections.addAll(strings, "one", "two", "three");