public Set<E> elementSet() {
      Set<E> es = elementSet;
      return (es == null) ? elementSet = createElementSet() : es;
    }

    @LazyInit @CheckForNull transient Set<Multiset.Entry<E>> entrySet;

    @SuppressWarnings("unchecked")
    @Override
    public Set<Multiset.Entry<E>> entrySet() {
      Set<Multiset.Entry<E>> es = entrySet;
      return (es == null)

  @LazyInit @CheckForNull private transient ImmutableSet<Entry<E>> entrySet;

  @Override
  public ImmutableSet<Entry<E>> entrySet() {
    ImmutableSet<Entry<E>> es = entrySet;
    return (es == null) ? (entrySet = createEntrySet()) : es;
  }

  private ImmutableSet<Entry<E>> createEntrySet() {
    return isEmpty() ? ImmutableSet.<Entry<E>>of() : new EntrySet();
  }

  abstract Entry<E> getEntry(int index);

   *
   * <p><b>Performance note:</b> the instance returned is a singleton.
   */
  @SuppressWarnings({"unchecked"}) // fully variant implementation (never actually produces any Es)
  public static <E> ImmutableSet<E> of() {
    return (ImmutableSet<E>) RegularImmutableSet.EMPTY;
  }

  /**
   * Returns an immutable set containing {@code element}. Preferred over {@link

      @Override
      public boolean add(@ParametricNullness E element) {
        throw new UnsupportedOperationException();
      }

      @Override
      public boolean addAll(Collection<? extends E> es) {
        throw new UnsupportedOperationException();
      }
    };
  }

  private static <E extends @Nullable Object> SortedSet<E> removeOnlySortedSet(
      final SortedSet<E> set) {