1. Proof rules dealing with fairness;Apt,1982
2. A cook's tour of countable nondeterminism;Apt,1981
3. Computable non-deterministic functions;Chandra;Proc. 19th Annual Symposium on Foundations of Computer Science,1978
4. A Discipline of Programming;Dijkstra,1976
5. Assigning meanings to programs;Floyd;Proc. AMS Symposium in Applied Mathematics,1967