@article {,
	title = {On the Reachability Problem for P Systems With Symport/Antiport},
	journal = {Publicationes Mathematicae Debrecen},
	volume = {65},
	year = {2004},
	pages = {603-627},
	address = {Debrecen, Hungr{\'\i}a},
	issn = {0033-3883},
	author = {Gheorghe Paun and Mario J. P{\'e}rez-Jim{\'e}nez and Fernando Sancho-Caparrini}
}
