Shankara Narayanan Krishna Raghavan Rama Kamala Krithivasan P Systems with Picture Objects. 53-74 2001 15 Acta Cybern. 1 http://www.inf.u-szeged.hu/kutatas/actacybernetica/vol15n1/cikk6.xml db/journals/actaC/actaC15.html#KrishnaRK01