(a) What does the code fragment compute and provide the corresponding post-assertion "Post"? (b) Follow the approach described in our handout (lect21.01.20-2.pdf) and lecture examplo on Program Correct- ness and Documentation: provide a loop invariant for the while-loop and prove its correctness (by placing appropriate assertions between all body/constituent statements). (e) Prove // Pre S // Post for the stated Pre-assertion with your provided Post-assertion in item (a). Code fragment Si: // Pre: integer N is defined and >= 0, and integer n = N. f - 1; 0) loop while not (n f :-fin; n: n - 1; end loop; // Post: Code fragment Se: // Pre: integers a and b are defined, and a >= 0 and b > 0. y = 0; while b