1. Berry, G., Boudol, G.: The chemical abstract machine. In: POPL 1990, pp. 81–94. ACM Press, New York (1990)
2. Csuhaj-Varju, E., Vaszil, G.: P automata. In: Păun, G., Rozenberg, G., Salomaa, A., Zandron, C. (eds.) WMC 2002. LNCS, vol. 2597, pp. 177–192. Springer, Heidelberg (2002)
3. Freund, R.: Special variants of P systems inducing an infinite hierarchy with respect to the number of membranes. Bulletin of the EATCS (75), 209–219 (2001)
4. Freund, R., Oswald, M.: A short note on analyzing P systems with antiport rules. Bulletin of EATCS 78, 231–236 (2002)
5. Lecture Notes in Computer Science;O.H. Ibarra,2003