1. Csuhaj-Varju, E., Ibarra, O., Vaszil, G.: On the computational complexity of P automata. In: Proc. DNA 10 (2004)
2. Dang, Z., Ibarra, O.: On P systems operating in sequential mode. Pre-Proc. DCFS 2004 (2004)
3. Freund, R.: Sequential P-systems (2000), Available at http://psystems.disco.unimib.it
4. Freund, R.: Asynchronous P systems. In: Mauri, G., Paun, G., Zandron, C. (eds.) Pre-Proc. Fifth Workshop on Membrane Computing (2004)
5. Freund, R., Paun, G.: On deterministic P systems (2003), See P Systems Web Page at http://psystems.disco.unimib.it