code: public static Comparator<LongTuple> comparator(Order order)
      {
          if (order == Order.LEXICOGRAPHICAL)
          {
              return (t0, t1) -> compareLexicographically(t0, t1);
          }
          if (order == Order.COLEXICOGRAPHICAL)
          {
              return (t0, t1) -> compareColexicographically(t0, t1);
          }
          return null;
      }
docs: Returns a comparator that compares tuples based on the specified
  {@link Order}. If the given order is <code>null</code>, then
  <code>null</code> will be returned.
  
  @param order The {@link Order}
  @return The comparator.