1. D. Bjørner, A ProCoS project description, ESPRIT BRA 3104, Bulletin of the EATCS 39 (1989) 60–73.
2. R.H. Campbell, A.N. Habermann, The specification of process synchronisation by path expressions, Lecture Notes in Comput. Sci. 16 (Springer-Verlag, 1974).
3. He Jifeng, Specification-oriented semantics for the ProCoS level 0 language, ProCoS Doc. Id. PRG/OU HJF 5/1, Oxford Univ., 1990.
4. He Jifeng, Specification-oriented semantics for the ProCoS programming language PLtime, ProCoS Doc. Id. PRG/OU HJF 7/2, Oxford Univ., 1991.
5. E.C.R. Hehner, Predicative programming, Comm. ACM 27 (2), 1984.