* iterated are the individual subsets created. Each of these subsets occupies an additional O(n)
   * memory but only for as long as the user retains a reference to it. That is, the set returned by
   * {@code combinations} does not retain the individual subsets.
   *
   * @param set the set of elements to take combinations of
   * @param size the number of elements per combination

          Derivative Works a copy of this License; and

      (b) You must cause any modified files to carry prominent notices
          stating that You changed the files; and

      (c) You must retain, in the Source form of any Derivative Works
          that You distribute, all copyright, patent, trademark, and
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          Derivative Works a copy of this License; and

      (b) You must cause any modified files to carry prominent notices
          stating that You changed the files; and

      (c) You must retain, in the Source form of any Derivative Works
          that You distribute, all copyright, patent, trademark, and
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   * as implementation details.
   */
  @J2ktIncompatible // serialization
  static class SerializedForm<K, V> implements Serializable {
    // This object retains references to collections returned by keySet() and value(). This saves
    // bytes when the both the map and its keySet or value collection are written to the same
    // instance of ObjectOutputStream.

          Derivative Works a copy of this License; and

      (b) You must cause any modified files to carry prominent notices
          stating that You changed the files; and

      (c) You must retain, in the Source form of any Derivative Works
          that You distribute, all copyright, patent, trademark, and
          attribution notices from the Source form of the Work,

          Derivative Works a copy of this License; and

      (b) You must cause any modified files to carry prominent notices
          stating that You changed the files; and

      (c) You must retain, in the Source form of any Derivative Works
          that You distribute, all copyright, patent, trademark, and
          attribution notices from the Source form of the Work,

          Derivative Works a copy of this License; and

      (b) You must cause any modified files to carry prominent notices
          stating that You changed the files; and

      (c) You must retain, in the Source form of any Derivative Works
          that You distribute, all copyright, patent, trademark, and
          attribution notices from the Source form of the Work,

   * as implementation details.
   */
  @J2ktIncompatible // serialization
  static class SerializedForm<K, V> implements Serializable {
    // This object retains references to collections returned by keySet() and value(). This saves
    // bytes when the both the map and its keySet or value collection are written to the same
    // instance of ObjectOutputStream.

          Derivative Works a copy of this License; and

      (b) You must cause any modified files to carry prominent notices
          stating that You changed the files; and

      (c) You must retain, in the Source form of any Derivative Works
          that You distribute, all copyright, patent, trademark, and
          attribution notices from the Source form of the Work,

          Derivative Works a copy of this License; and

      (b) You must cause any modified files to carry prominent notices
          stating that You changed the files; and

      (c) You must retain, in the Source form of any Derivative Works
          that You distribute, all copyright, patent, trademark, and
          attribution notices from the Source form of the Work,