BiMap<K, V> unfiltered() {
      return (BiMap<K, V>) unfiltered;
    }

    @Override
    @CheckForNull
    public V forcePut(@ParametricNullness K key, @ParametricNullness V value) {
      checkArgument(apply(key, value));
      return unfiltered().forcePut(key, value);
    }

    @Override
    public BiMap<V, K> inverse() {
      return inverse;
    }

    @Override