code: public static Quarters between(CalendarQuarter q1, CalendarQuarter q2) {
  
          PlainDate d1 = q1.atDayOfQuarter(1);
          PlainDate d2 = q2.atDayOfQuarter(1);
          return Quarters.between(d1, d2);
  
      }
docs: /*[deutsch]
  <p>Bestimmt die Differenz zwischen den angegebenen Quartalen. </p>
  
  @param   q1  first quarter year
  @param   q2  second quarter year
  @return  difference in quarter years