Assignment 3 has been graded. It will be handed back tomorrow.
Each question worths 10 marks. Total = 50.
General comments:
1. Please pay attention to the lectures and read the lecture notes
carefully.
2. Please read the assignment questions carefully.
3. Did I say please read the assignment questions carefully? What is
the business with discussing what would happen to your programs for
n<0, when n is stated in the questions to be natural?
4. You should exercise extreme care when you deal with the sequential
composition operator (the semicolon). Please do not deviate from
the exact definition and the substitution law.
Detailed marking scheme:
1. If attempt to prove, at most 6 marks.
If disproof is weak (e.g., counterexample not concrete enough, or
counterexample not proved to be a counterexample), at most 7 marks.
2. proof of first refinement = 3 marks
proof of second refinement = 7 marks
3. program = 4 marks
time claims = 2 marks
proof = 4 marks
4. state refinements (s' has the right value) = 5 marks
time refinements (t'-t has the right upper bound) = 5 marks
Both require stating *all* specifications, including intermediate ones.
5. Putting in t:=t+1's = 1 mark
Exponential time claim = 4 marks
Proof = 5 marks
-- Albert