code: public static Years<Weekcycle> between(CalendarWeek w1, CalendarWeek w2) {
  
          int delta = w2.getYear() - w1.getYear();
  
          if (delta > 0) {
              if (w2.getWeek() < w1.getWeek()) {
                  delta--;
              }
          } else if (delta < 0) {
              if (w2.getWeek() > w1.getWeek()) {
                  delta++;
              }
          }
  
          return Years.ofWeekBased(delta);
  
      }
docs: /*[deutsch]
  <p>Bestimmt die Jahresdifferenz zwischen den angegebenen Kalenderwochen. </p>
  
  @param   w1  first calendar week
  @param   w2  second calendar week
  @return  year difference