* ForwardingMap#keySet} to forward to this implementation or a subclass thereof.
   *
   * @since 10.0
   */
  protected class StandardKeySet extends Maps.KeySet<K, V> {
    /** Constructor for use by subclasses. */
    public StandardKeySet() {
      super(ForwardingMap.this);
    }
  }

  /**
   * A sensible, albeit inefficient, definition of {@link #containsKey} in terms of the {@code

      return standardEquals(object);
    }

    @Override
    public int hashCode() {
      return standardHashCode();
    }

    @Override
    public Set<K> keySet() {
      return new StandardKeySet();
    }

    @Override
    public Collection<V> values() {
      return new StandardValues();
    }

    @Override
    public String toString() {
      return standardToString();
    }