Question 6 [6] Lists can be used to represent sets in Prolog. Write a Prolog procedure that can be used to perform the following operation: The symmetric difference between two sets A and B can be defined as the set of elements that either belong to A or to B, but not to both. Use this definition to write a Prolog procedure symdiff (A, B, R) that returns the symmetric difference R between A and B. (Hint: Use the built-in Prolog predicate bagof.)