return set;
    }
    return new UnmodifiableNavigableSet<>(set);
  }

  static final class UnmodifiableNavigableSet<E extends @Nullable Object>
      extends ForwardingSortedSet<E> implements NavigableSet<E>, Serializable {
    private final NavigableSet<E> delegate;
    private final SortedSet<E> unmodifiableDelegate;

    UnmodifiableNavigableSet(NavigableSet<E> delegate) {

  }

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

  @Override
  NavigableSet<E> createElementSet() {
    return Sets.unmodifiableNavigableSet(delegate().elementSet());
  }

  @Override
  public NavigableSet<E> elementSet() {
    return (NavigableSet<E>) super.elementSet();
  }

  }

  @Override
  <E extends @Nullable Object> SortedSet<E> unmodifiableCollectionSubclass(
      Collection<E> collection) {
    if (collection instanceof NavigableSet) {
      return Sets.unmodifiableNavigableSet((NavigableSet<E>) collection);
    } else {
      return Collections.unmodifiableSortedSet((SortedSet<E>) collection);
    }
  }

  @Override

  }

  @Override
  <E extends @Nullable Object> SortedSet<E> unmodifiableCollectionSubclass(
      Collection<E> collection) {
    if (collection instanceof NavigableSet) {
      return Sets.unmodifiableNavigableSet((NavigableSet<E>) collection);
    } else {
      return Collections.unmodifiableSortedSet((SortedSet<E>) collection);
    }
  }

  @Override

                    return Sets.unmodifiableNavigableSet(set);
                  }

                  @Override
                  public List<String> order(List<String> insertionOrder) {
                    return Ordering.natural().sortedCopy(insertionOrder);
                  }
                })
            .named("Sets.unmodifiableNavigableSet[TreeSet]")
            .withFeatures(

                NavigableSet<String> innerSet = new TreeSet<>();
                Collections.addAll(innerSet, elements);
                return Collections.unmodifiableNavigableSet(innerSet);
              }
            })
        .named("unmodifiableNavigableSet/TreeSet, natural")
        .withFeatures(
            CollectionFeature.KNOWN_ORDER,
            CollectionFeature.RESTRICTS_ELEMENTS,

                    return Sets.unmodifiableNavigableSet(set);
                  }

                  @Override
                  public List<String> order(List<String> insertionOrder) {
                    return Ordering.natural().sortedCopy(insertionOrder);
                  }
                })
            .named("Sets.unmodifiableNavigableSet[TreeSet]")
            .withFeatures(

          .put(ImmutableSet.class, ImmutableSet.of())
          .put(SortedSet.class, ImmutableSortedSet.of())
          .put(ImmutableSortedSet.class, ImmutableSortedSet.of())
          .put(NavigableSet.class, Sets.unmodifiableNavigableSet(Sets.newTreeSet()))
          .put(Map.class, ImmutableMap.of())
          .put(ImmutableMap.class, ImmutableMap.of())
          .put(SortedMap.class, ImmutableSortedMap.of())

          .put(ImmutableSet.class, ImmutableSet.of())
          .put(SortedSet.class, ImmutableSortedSet.of())
          .put(ImmutableSortedSet.class, ImmutableSortedSet.of())
          .put(NavigableSet.class, Sets.unmodifiableNavigableSet(Sets.newTreeSet()))
          .put(Map.class, ImmutableMap.of())
          .put(ImmutableMap.class, ImmutableMap.of())
          .put(SortedMap.class, ImmutableSortedMap.of())

    }

    @Override
    <E extends @Nullable Object> Collection<E> unmodifiableCollectionSubclass(
        Collection<E> collection) {
      if (collection instanceof NavigableSet) {
        return Sets.unmodifiableNavigableSet((NavigableSet<E>) collection);
      } else if (collection instanceof SortedSet) {
        return Collections.unmodifiableSortedSet((SortedSet<E>) collection);
      } else if (collection instanceof Set) {