Gabriel Ciobanu Gheorghe Paun Mario J. Pérez-Jiménez On the Branching Complexity of P Systems. 27-36 2006 73 Fundam. Inform. 1-2 http://iospress.metapress.com/content/d4jvv3k3tmtx301e/ db/journals/fuin/fuin73.html#CiobanuPP06