* @throws IllegalArgumentException Wenn die gegebenen Anzahlen ungültig sind oder zu einer ungültigen Gesamtanzahl führen würde. */
	public static int durationmonthsOf(final int years, final int months) throws IllegalArgumentException {
		FEMDuration._checkYears_(+years);
		FEMDuration._checkYears_(-years);
		FEMDuration._checkMonths_(-months);
		FEMDuration._checkMonths_(+months);
		final int result = FEMDuration._durationmonthsOf_(years, months);
		FEMDuration._checkMonths_(+result);
		FEMDuration._checkMonths_(-result);
		return result;
	}