internal SchoolSubject(PlainText name, Proportion examProportion, List <Student> registeredStudents, SchoolSubjectState subjectState, Credits credits)
     : this(name, subjectState, credits)
 {
     ExamProportion      = examProportion;
     _registeredStudents = registeredStudents;
 }
 internal SchoolSubject(PlainText name, SchoolSubjectState subjectState, Credits credits)
 {
     Name         = name;
     State        = subjectState;
     this.credits = credits;
 }