SortedSet<String> set = of("e", "a", "f", "b", "d", "c");
    SortedSet<String> subset = set.subSet("c", "e");
    SortedSet<String> copy = copyOf(subset);
    assertEquals(subset, copy);
  }

  public void testCopyOf_headSet() {
    SortedSet<String> set = of("e", "a", "f", "b", "d", "c");
    SortedSet<String> headset = set.headSet("d");
    SortedSet<String> copy = copyOf(headset);

    ms.add("a", 1);
    ms.add("b", 3);
    ms.add("c", 2);
    ms.add("d", 1);
    ms.add("e", 3);
    ms.add("f", 2);

    SortedSet<String> elementSet = ms.elementSet();
    assertThat(elementSet).containsExactly("a", "b", "c", "d", "e", "f").inOrder();
    SortedSet<String> subset = elementSet.subSet("b", "f");
    assertThat(subset).containsExactly("b", "c", "d", "e").inOrder();

    assertTrue(subset.remove("c"));

    SortedSet<String> set = of("e", "a", "f", "b", "d", "c");
    SortedSet<String> subset = set.subSet("c", "e");
    SortedSet<String> copy = copyOf(subset);
    assertEquals(subset, copy);
  }

  public void testCopyOf_headSet() {
    SortedSet<String> set = of("e", "a", "f", "b", "d", "c");
    SortedSet<String> headset = set.headSet("d");
    SortedSet<String> copy = copyOf(headset);

        delegate.subSet(
            checkValid(fromElement), fromInclusive, checkValid(toElement), toInclusive));
  }

  @Override
  public SortedSet<E> subSet(E fromElement, E toElement) {
    return subSet(fromElement, true, toElement, false);
  }

  @Override
  public SortedSet<E> tailSet(E fromElement) {
    return tailSet(fromElement, true);
  }

  @Override

        delegate.subSet(
            checkValid(fromElement), fromInclusive, checkValid(toElement), toInclusive));
  }

  @Override
  public SortedSet<E> subSet(E fromElement, E toElement) {
    return subSet(fromElement, true, toElement, false);
  }

  @Override
  public SortedSet<E> tailSet(E fromElement) {
    return tailSet(fromElement, true);
  }

  @Override

  }

  public void testFirst_sortedSet() {
    SortedSet<String> sortedSet = ImmutableSortedSet.of("b", "c", "a");
    assertThat(FluentIterable.from(sortedSet).first()).hasValue("a");
  }

  public void testFirst_emptySortedSet() {
    SortedSet<String> sortedSet = ImmutableSortedSet.of();
    assertThat(FluentIterable.from(sortedSet).first()).isAbsent();
  }

  public void testFirst_iterable() {

    }

    @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) {

    }

    @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) {

      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

      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