@article {610, title = {Length of rules and tractability in tissue-like P systems}, journal = {Algebraic Computing, Soft Computing, and Program Verification}, year = {2010}, month = {April 2010}, address = {Castro Urdiales, Spain}, url = {http://www.gimac.uma.es/hard\&soft2010/Home.html}, author = {Agust{\'\i}n Riscos-N{\'u}{\~n}ez and Ignacio P{\'e}rez-Hurtado} }