Course A: Normal course in which John Smith (a student) is enrolled
Course B: Normal course in which John Smith is enrolled too
Course M: Meta course in which A & B courses are enrolled (so that John Smith is enrolled also in M course)
A teacher in course B unroll John Smith from his course
John Smith is also unrolled from M course, but I still want John in course M because he is still enrolled in course A.
A teacher in course A unrolls and rolls again John