if (!contains(key)) {
        return false;
      }
      removeFromBothMaps(key);
      return true;
    }

    @Override
    public boolean removeAll(Collection<?> keysToRemove) {
      return standardRemoveAll(keysToRemove);
    }

    @Override
    public boolean retainAll(Collection<?> keysToRetain) {
      return standardRetainAll(keysToRetain);
    }

      if (!contains(key)) {
        return false;
      }
      removeFromBothMaps(key);
      return true;
    }

    @Override
    public boolean removeAll(Collection<?> keysToRemove) {
      return standardRemoveAll(keysToRemove);
    }

    @Override
    public boolean retainAll(Collection<?> keysToRetain) {
      return standardRetainAll(keysToRetain);
    }