1. Aschcroft, E. A. and Z. Manna. "Formalization of Properties of Parallel Programs." Machine Intelligence 6, Edinburgh University Press.
2. Dijkstra, E. W. "Guarded Commands, Nondeterminacy and Formal Derivation of Programs," C.A.C.M. 18, 8, 1975.
3. Fischer, M. J. and R. E. Ladner. "Propositional Modal Logic of Programs," Proc. 9th ann. ACM Symp. on Theory of Computing, 286–294, Boulder, Col., May, 1977.
4. Floyd, R. W. "Assigning Meaning to Programs," Proc. AMS Symp. Appl. Math. 19, 1967, 19–32.
5. Harel, D. and V. R. Pratt. "Nondeterminism in Logics of Programs," Proc. 5th ann ACM Symp. on Principles of Prog. Lang., 203–213, Tuscon, Arizona, Jan., 1978.