return delegate().forcePut(key, value);
      }
    }

    @Override
    public BiMap<V, K> inverse() {
      synchronized (mutex) {
        if (inverse == null) {
          inverse = new SynchronizedBiMap<>(delegate().inverse(), mutex, this);
        }
        return inverse;
      }
    }

    private static final long serialVersionUID = 0;
  }