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;
    @LazyInit transient @Nullable Set<V> values;

    UnmodifiableBiMap(BiMap<? extends K, ? extends V> delegate, @Nullable BiMap<V, K> inverse) {

      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;
    @LazyInit transient @Nullable Set<V> values;

    UnmodifiableBiMap(BiMap<? extends K, ? extends V> delegate, @Nullable BiMap<V, K> inverse) {

    for (Object key : keys) {
      remove(key);
    }
  }

  @LazyInit @RetainedWith @Nullable Set<K> keySet;

  @Override
  public Set<K> keySet() {
    // does not impact recency ordering
    Set<K> ks = keySet;
    return (ks != null) ? ks : (keySet = new KeySet());
  }

  @LazyInit @RetainedWith @Nullable Collection<V> values;

  @Override