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 225-250. Berlin, Heidelberg, New York: Springer-Verlag, 1980.
Also: An Operational Characterisation of the Atomicity of Activities. University of Newcastle upon Tyne, Computing Laboratory, Technical Report 147, January 1980.