}

  /**
   * @see Maps#unmodifiableBiMap(BiMap)
   */
  private static final class UnmodifiableBiMap<
          K extends @Nullable Object, V extends @Nullable Object>
      extends ForwardingMap<K, V> implements BiMap<K, V>, Serializable {
    final Map<K, V> unmodifiableMap;
    final BiMap<? extends K, ? extends V> delegate;
    @LazyInit @RetainedWith @Nullable BiMap<V, K> inverse;

  }

  /**
   * @see Maps#unmodifiableBiMap(BiMap)
   */
  private static final class UnmodifiableBiMap<
          K extends @Nullable Object, V extends @Nullable Object>
      extends ForwardingMap<K, V> implements BiMap<K, V>, Serializable {
    final Map<K, V> unmodifiableMap;
    final BiMap<? extends K, ? extends V> delegate;
    @LazyInit @RetainedWith @Nullable BiMap<V, K> inverse;