@Override
    public String toString() {
      return "(" + left + ", " + right + ")";
    }
  }

  static class SortedMapDifferenceImpl<K extends @Nullable Object, V extends @Nullable Object>
      extends MapDifferenceImpl<K, V> implements SortedMapDifference<K, V> {
    SortedMapDifferenceImpl(
        SortedMap<K, V> onlyOnLeft,
        SortedMap<K, V> onlyOnRight,
        SortedMap<K, V> onBoth,

    @Override
    public String toString() {
      return "(" + left + ", " + right + ")";
    }
  }

  static class SortedMapDifferenceImpl<K extends @Nullable Object, V extends @Nullable Object>
      extends MapDifferenceImpl<K, V> implements SortedMapDifference<K, V> {
    SortedMapDifferenceImpl(
        SortedMap<K, V> onlyOnLeft,
        SortedMap<K, V> onlyOnRight,
        SortedMap<K, V> onBoth,