Oana Andrei Gabriel Ciobanu Dorel Lucanu Executable Specifications of P Systems. 126-145 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3365&spage=126 2004 conf/membrane/2004 Workshop on Membrane Computing db/conf/membrane/membrane2004.html#AndreiCL04