* remain as implementation details.
   */
  @J2ktIncompatible // serialization
  private static class SerializedForm<K, V> extends ImmutableMap.SerializedForm<K, V> {
    private final Comparator<? super K> comparator;

    SerializedForm(ImmutableSortedMap<K, V> sortedMap) {
      super(sortedMap);
      comparator = sortedMap.comparator();
    }

    @Override

   * remain as implementation details.
   */
  @J2ktIncompatible // serialization
  private static class SerializedForm<K, V> extends ImmutableMap.SerializedForm<K, V> {
    private final Comparator<? super K> comparator;

    SerializedForm(ImmutableSortedMap<K, V> sortedMap) {
      super(sortedMap);
      comparator = sortedMap.comparator();
    }

    @Override