A course number may not be reused for a new course for a period of three years for undergraduate courses and five years for graduate courses. This rule is designed to avoid confusion among faculty and students and to avoid the need for variances if students who have taken the old course wish to take the new course. (The time restriction is based on the latter consideration and represents the time in which most students enrolled at the time of the change will have left the University.) This rule applies whether a course has been withdrawn or simply has not been offered during the restricted time period. Use of a suffix with a new course may avoid the above problems – course 101 is considered to be different from course 101A and similarly 101C from 101D.