R. Freund, S. Verlan:
"A formal framework for P systems";
Talk: Workshop on Membrane Computing, Thessaloniki; 2007-06-25 - 2007-06-28; in: "Eighth Workshop on Membane Computing (WMC8)", G. Eleftherakis, P. Kefalas, Gh. Paun (ed.); South-East European Research Centre, (2007), ISBN: 978-960-89629-2-7; 317 - 330.