* import static java.util.Comparator.naturalOrder;
 *
 * ...
 *   private static final Comparator<Foo> COMPARATOR =
 *       comparing((Foo foo) -> foo.aString)
 *           .thenComparing(foo -> foo.anInt)
 *           .thenComparing(foo -> foo.anEnum, nullsLast(naturalOrder()));
 *
 *   @Override
 *   public int compareTo(Foo that) {
 *     return COMPARATOR.compare(this, that);
 *   }
 * }
 *

   * serializable.
   *
   * <p><b>Java 8+ users:</b> Use {@code thisComparator.thenComparing(secondaryComparator)} instead.
   * Depending on what {@code secondaryComparator} is, one of the other overloads of {@code
   * thenComparing} may be even more useful.
   */
  public <U extends T> Ordering<U> compound(Comparator<? super U> secondaryComparator) {