public function addYears(int $years, string $qualifier = ''): Date
    {
        $tmp               = clone $this;
        $tmp->date1->year  += $years;
        $tmp->date1->month = 0;
        $tmp->date1->day   = 0;
        $tmp->date1->setJdFromYmd();
        $tmp->qual1 = $qualifier;
        $tmp->qual2 = '';
        $tmp->date2 = null;

        return $tmp;
    }