public static boolean checkFor0Points(Data myData) {
        //0 points only allowed in "none" semesters
        for(Subject thisSubject:myData.subjects){
            for(Semester thisSemester:thisSubject.semesters){
                if (thisSemester.mark==0 && thisSemester.usedState!=UsedState.none)
                    return false;
            }
        }
        return true;
    }