Reference

      1. Gianfranco Balbo, "Introductory Tutorial Petri Nets", 21st International Conference on Application and Theory of Petri Nets.
      2. Marc Boyer and Michel Diaz, "Multiple Enabledness of Transitions in Petri Nets with Time",
        31077 Toulouse Cedex 4 France. [PS]
      3. Bohuslav Krena, "Type Analysis in Object-Oriented Petri Nets". [PDF]
      4. BKurt Jensen, "A Brief Introduction to Coloured Petri Nets", Computer Science Department, University of Aarhus. [PDF]
      5. Bo Lindstrøm and Lisa Wells, "Annotating Coloured Petri Nets", Department of Computer Science, University of Aarhus. [PDF]
      6. Michael Weber, "Tool Support for Various Types of Petr Nets", Petri Net Technologies for Modelling Communication Based Systems, pages 171-178.