1. Narinyani, A.S. Theory of parallel programming: Formal Models, Advances in Information Systems Sciences, 6, Plenum Press, New York, 1976.
2. Mazurkiewicz, A. Invariants of Concurrent Programs, Infopol Conference Proc., Warsaw, 1976.
3. Winkowski, T. On Algebraic Characterization of the Behavior of Non-Sequential Systems, Information Processing Letters, 6, No. 4, 1977, 105–109.
4. Campbell, R.H., Habermann, A.N. The Specification of Process Synchronization by Path Expressions, Springer Lecture Notes on Computer Science, 16, Berlin, 1974.
5. Lauer, P.E., Campbell, R.H. Formal Semantics for a Class of High-level Primitives for Coordinating of Concurrent Processes, Acta Informatica, No. 5, 1975, 297–332.