1. Janicki R., An Algebraic Characterization of Concurrency Relations, Information Processing Letters, to appear.
2. Mazurkiewicz A., Invariants of Concurrent Programs, Proc. of IFIP-INFOPOL Conf. on Information Processing, North Holland, 1977,353–372.
3. Mazurkiewicz A., Concurrent Program Schemes and their Interpretations, DAIMI-PB-78, Aarhus University Publ., 1977.
4. Petri C.A., Concepts of Net Theory, MFCS`73 Proceedings, High Tatras, Math. Inst. of Slovak Acad. of Sci., 1973, 137–146.
5. ISF Report;C. A. Petri,1975