public int hashCode() {
    return Sets.hashCodeImpl(entrySet());
  }

  @Override
  public String toString() {
    return entrySet().toString();
  }

  /** @since 21.0 (present with return type {@code Set} since 2.0) */
  @Override
  public abstract ImmutableSet<E> elementSet();

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

  @Override