Membrane computing : 8th International Workshop, WMC 2007 Thessaloniki, Greece, June 25-28, 2007 Revised Selected and Invited Papers - Kefalas, Petros; Salomaa, Arto; Paun, Gheorghe; Rozenberg, Grzegorz; Eleftherakis, George; Salomaa, Arto (Lecture Notes in Computer Science,, 2007)