@article {1793, title = {The Role of the Direction in Tissue P Systems with Cell Separation}, journal = {Journal of Automata, Languages and Combinatorics}, volume = { 19 (2014) 1{\textendash}4}, year = {2014}, pages = {185{\textendash}199}, issn = {1430-189X}, author = {Luis F. Mac{\'\i}as-Ramos and Miguel A. Mart{\'\i}nez-del-Amor and Mario J. P{\'e}rez-Jim{\'e}nez and Agust{\'\i}n Riscos-N{\'u}{\~n}ez and Luis Valencia-Cabrera} }