Map<K, V1> fromMap, EntryTransformer<? super K, ? super V1, V2> transformer) {
    return new TransformedEntriesMap<>(fromMap, transformer);
  }

  /**
   * Returns a view of a sorted map whose values are derived from the original sorted map's entries.
   * In contrast to {@link #transformValues}, this method's entry-transformation logic may depend on
   * the key as well as the value.
   *