1. Best, E.: Structure Theory of Petri Nets: the Free Choice Hiatus, Advanced Course on Petri Nets, Bad Honnef, Lecture Notes on Computer Science 254–255, Springer (1987).
2. Campos, J; Chiola, G.: Private communication (1989).
3. Esparza, J.; Silva, M.: Top-down Synthesis of Live & Bounded Free Choice Nets. To appear in: Proceedings of the XI International Conference on Applications and Theory of Petri Nets, Paris (June 1990).
4. Esparza, J.: Structure Theory of Free Choice nets. Ph.D. Thesis, University of Zaragoza (June 1990).
5. Genrich, H.; Thiagarajan, P.S.: A theory of bipolar synchronisation schemes, Theoretical Computer Science, 30, pp. 241–318 (1984).