code: public static CalendarPeriod<CalendarYear> between(
          CalendarYear y1,
          CalendarYear y2
      ) {
  
          return new FixedCalendarPeriod<>(y1, y2, FixedCalendarTimeLine.forYears());
  
      }
docs: /*[deutsch]
  Erzeugt eine {@code CalendarPeriod} f&uuml;r die angegebene Jahresspanne.
  
  @param   y1  first calendar year
  @param   y2  last calendar year (inclusive)
  @return  CalendarPeriod