return CollectCollectors.flatteningToImmutableSetMultimap(keyFunction, valuesFunction);
  }

  /**
   * Returns the empty multimap.
   *
   * <p><b>Performance note:</b> the instance returned is a singleton.
   */
  // Casting is safe because the multimap will never hold any elements.
  @SuppressWarnings("unchecked")
  public static <K, V> ImmutableSetMultimap<K, V> of() {

    return CollectCollectors.toImmutableBiMap(keyFunction, valueFunction);
  }

  /**
   * Returns the empty bimap.
   *
   * <p><b>Performance note:</b> the instance returned is a singleton.
   */
  // Casting to any type is safe because the set will never hold any elements.
  @SuppressWarnings("unchecked")
  public static <K, V> ImmutableBiMap<K, V> of() {

      return new RegularImmutableSortedSet<>(ImmutableList.of(), comparator);
    }
  }

  /**
   * Returns the empty immutable sorted set.
   *
   * <p><b>Performance note:</b> the instance returned is a singleton.
   */
  @SuppressWarnings("unchecked") // The natural-ordered empty set supports all types.
  public static <E> ImmutableSortedSet<E> of() {
    return (ImmutableSortedSet<E>) RegularImmutableSortedSet.NATURAL_EMPTY_SET;

   * specified by the given {@code builder}. The returned {@link MapMakerInternalMap} will be
   * optimized to saved memory. Since {@link MapMaker.Dummy} is a singleton, we don't need to store
   * any values at all. Because of this optimization, {@code build.getValueStrength()} must be
   * {@link Strength#STRONG}.
   *

    multiset.add(checkNotNull(elementFunction.apply(t)), countFunction.applyAsInt(t));
  }

  /**
   * Returns the empty immutable sorted multiset.
   *
   * <p><b>Performance note:</b> the instance returned is a singleton.
   */
  @SuppressWarnings("unchecked")
  public static <E> ImmutableSortedMultiset<E> of() {
    return (ImmutableSortedMultiset) RegularImmutableSortedMultiset.NATURAL_EMPTY_MULTISET;
  }

   * Collections#emptyList}, and is preferable mainly for consistency and maintainability of your
   * code.
   *
   * <p><b>Performance note:</b> the instance returned is a singleton.
   */
  // Casting to any type is safe because the list will never hold any elements.
  @SuppressWarnings("unchecked")
  public static <E> ImmutableList<E> of() {
    return (ImmutableList<E>) EMPTY;
  }

  /**

                CollectionFeature.ALLOWS_NULL_QUERIES)
            .createTestSuite());

    suite.addTestSuite(ImmutableSortedSetTest.class);

    return suite;
  }

  // enum singleton pattern
  private enum StringLengthComparator implements Comparator<String> {
    INSTANCE;

    @Override
    public int compare(String a, String b) {
      return a.length() - b.length();
    }
  }

   * specified by the given {@code builder}. The returned {@link MapMakerInternalMap} will be
   * optimized to saved memory. Since {@link MapMaker.Dummy} is a singleton, we don't need to store
   * any values at all. Because of this optimization, {@code build.getValueStrength()} must be
   * {@link Strength#STRONG}.
   *

      return new RegularImmutableSortedSet<>(ImmutableList.of(), comparator);
    }
  }

  /**
   * Returns the empty immutable sorted set.
   *
   * <p><b>Performance note:</b> the instance returned is a singleton.
   */
  @SuppressWarnings("unchecked") // The natural-ordered empty set supports all types.
  public static <E> ImmutableSortedSet<E> of() {
    return (ImmutableSortedSet<E>) RegularImmutableSortedSet.NATURAL_EMPTY_SET;

   * Collections#emptyMap}, and is preferable mainly for consistency and maintainability of your
   * code.
   *
   * <p><b>Performance note:</b> the instance returned is a singleton.
   */
  @SuppressWarnings("unchecked")
  public static <K, V> ImmutableMap<K, V> of() {
    return (ImmutableMap<K, V>) RegularImmutableMap.EMPTY;
  }

  /**