// TreeSet

  /**
   * Creates a <i>mutable</i>, empty {@code TreeSet} instance sorted by the natural sort ordering of
   * its elements.
   *
   * <p><b>Note:</b> if mutability is not required, use {@link ImmutableSortedSet#of()} instead.
   *
   * <p><b>Note:</b> this method is now unnecessary and should be treated as deprecated. Instead,
   * use the {@code TreeSet} constructor directly, taking advantage of <a

  }

  /**
   * Returns an {@code ImmutableSortedSet} containing all of the elements from this {@code
   * FluentIterable} in the order specified by {@code comparator}, with duplicates (determined by
   * {@code comparator.compare(x, y) == 0}) removed. To produce an {@code ImmutableSortedSet} sorted
   * by its natural ordering, use {@code toSortedSet(Ordering.natural())}.
   *

 *       how the collection was created. Typically this is insertion order unless an explicit
 *       ordering is otherwise specified (e.g. {@link ImmutableSortedSet#naturalOrder}). See the
 *       appropriate factory method for details. View collections such as {@link
 *       ImmutableMultiset#elementSet} iterate in the same order as the parent, except as noted.

 *       how the collection was created. Typically this is insertion order unless an explicit
 *       ordering is otherwise specified (e.g. {@link ImmutableSortedSet#naturalOrder}). See the
 *       appropriate factory method for details. View collections such as {@link
 *       ImmutableMultiset#elementSet} iterate in the same order as the parent, except as noted.

      fail();
    } catch (UnsupportedOperationException expected) {
    }
  }

  @GwtIncompatible // NavigableMap
  public void testAsMapNavigableEmpty() {
    NavigableSet<String> strings = ImmutableSortedSet.of();
    NavigableMap<String, Integer> map = Maps.asMap(strings, LENGTH_FUNCTION);
    assertThat(map.entrySet()).isEmpty();
    assertTrue(map.isEmpty());
    assertNull(map.get("five"));
  }

      fail();
    } catch (UnsupportedOperationException expected) {
    }
  }

  @GwtIncompatible // NavigableMap
  public void testAsMapNavigableEmpty() {
    NavigableSet<String> strings = ImmutableSortedSet.of();
    NavigableMap<String, Integer> map = Maps.asMap(strings, LENGTH_FUNCTION);
    assertThat(map.entrySet()).isEmpty();
    assertTrue(map.isEmpty());
    assertNull(map.get("five"));
  }

  public static <E extends Comparable<? super E>> ImmutableSortedMultiset<E> of(E element) {
    RegularImmutableSortedSet<E> elementSet =
        (RegularImmutableSortedSet<E>) ImmutableSortedSet.of(element);
    long[] cumulativeCounts = {0, 1};
    return new RegularImmutableSortedMultiset<>(elementSet, cumulativeCounts, 0, 1);
  }

  /**