1. Alhazov, A., Martin-Vide, C., Pan, L.: Solving a PSPACE-complete problem by recognizing P systems with restricted active membranes. Fundamenta Informaticae 58(2), 66–77 (2003)
2. Cavaliere, M.: Time-free solution to hard computational problems. Proc. Tenth Brainstorming Week Membr. Comput. 1, 204–210 (2012)
3. Cavaliere, M., Deufemia, V.: Further results on time-free P systems. Int. J. Found. Comput. Sci. 17(1), 69–89 (2006)
4. Ciobanu, G., Pérez-Jiménez, M.J., Păun, G.: Applications of Membrane Computing. Springer, Berlin (2006)
5. Lecture Notes in Computer Science;M Cavaliere,2005