return transformEntries(fromMultimap, transformer);
  }

  /**
   * Returns a view of a multimap whose values are derived from the original multimap's entries. In
   * contrast to {@link #transformValues}, this method's entry-transformation logic may depend on
   * the key as well as the value.
   *
   * <p>All other properties of the transformed multimap, such as iteration order, are left intact.

   */
  public static <T extends @Nullable Object> Iterator<T> concat(
      Iterator<? extends Iterator<? extends T>> inputs) {
    return new ConcatenatedIterator<>(inputs);
  }

  /** Concats a varargs array of iterators without making a defensive copy of the array. */
  static <T extends @Nullable Object> Iterator<T> concatNoDefensiveCopy(
      Iterator<? extends T>... inputs) {

   */
  public static <T extends @Nullable Object> Iterator<T> concat(
      Iterator<? extends Iterator<? extends T>> inputs) {
    return new ConcatenatedIterator<>(inputs);
  }

  /** Concats a varargs array of iterators without making a defensive copy of the array. */
  static <T extends @Nullable Object> Iterator<T> concatNoDefensiveCopy(
      Iterator<? extends T>... inputs) {