In: Brauer, W.: Lecture Notes in Computer Science, Vol. 84: Net Theory and Applications, Proc. of the Advanced Course on General Net Theory of Processes and Systems, Hamburg, 1979, pages 291-305. Berlin, Heidelberg, New York: Springer-Verlag, 1980.
Also in: Extended Version: Theoretical Computer Science 18, No. 2, pages 149-171. 1982.