code: public HijriCalendar minus(
          int amount,
          Unit unit
      ) {
  
          return this.plus(MathUtils.safeNegate(amount), unit);
  
      }
docs: /*[deutsch]
  <p>Subtrahiert die angegebenen Zeiteinheiten von dieser Instanz. </p>
  
  @param   amount      amount to be subtracted (maybe negative)
  @param   unit        calendrical unit
  @return  result of subtraction as changed copy, this instance remains unaffected
  @throws  ArithmeticException in case of numerical overflow
  @since   3.14/4.10