1. E. Best, "Structure Theory of Nets: the Free Choice Hiatus", Lecture Notes in Computer Science 254, Springer Verlag (1986).
2. J. Hall, R. Hopkins, O. Botti, F. DeCindio, "A Petri Net Semantics of Occam", Technical Report, Computing Laboratory, University of Newcastle upon Tyne, (1990).
3. W. Reisig, "Place/Transition Systems", Lecture Notes in Computer Science 254, Springer Verlag (1986).
4. V.E. Kotov, "An Algebra for Parallelism based on Petri Nets", in J. Winkowski (ed.) Mathematical Foundations of Computer Science, Lecture Notes in Computer Science 64, Springer Verlag (1978).
5. R.P. Hopkins and J. Hall, "Towards a Petri Net Programming Notation", Technical Memorandum, ESPRIT BRA 3148 DEMON (1990).