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COMP3151/9154 Homework 6
发布时间:2023-08-28
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COMP3151/9154
Homework (Week 7)
Due: 9am Mon 17 July 2023
1. Non-compositional Verification: Here is a three process message pass- ing system presented as a transition diagram of three processes P1 , P2 , and P3 .
Prove using the Levin and Gries or AFR methods that the following Hoare triple holds:
{True} P1 ∥ P2 ∥ P3 {y = v − 1}
Give your assertion networks, your extra auxiliary variables, and (if us- ing AFR) your communication invariant. List and discharge the proof obligations.
2. Termination: Consider the following program:
(a) Use the local method to prove x ≥ 0 -convergence for this program. You’ll need exit locations for p and q (not shown in the above pseu- docode). First specify your assertion networks, your wellfounded set, and your ranking functions. Then list and discharge the proof obli- gations.
(b) Is this program 」-convergent? Briefly motivate your answer. (c) Is this program T-convergent? Briefly motivate your answer.
You may assume that the x := x — 1 and x := 2(x are executed atomically.