public void changeteacher_of_exist_course(course co, Teacher newte)
{
co.changeTeacher(co, newte);
}
public void printinfo_of_exist_course(course co)
{
co.printcourseinfo(co);
}
public void addstudent_to_existcourse(Student st, course co)
{
co.addstudent(st);
}
public void removestudent_to_existcourse(Student st, course co)
{
co.removestudent(st);
}
public void changeTeacher(course co, Teacher newte)
{
co.teacher = newte;
}