Alberto Leporati Claudio Zandron Claudio Ferretti Giancarlo Mauri Solving Numerical NP-Complete Problems with Spiking Neural P Systems. 336-352 2007 conf/membrane/2007 Workshop on Membrane Computing http://dx.doi.org/10.1007/978-3-540-77312-2_21 db/conf/membrane/membrane2007.html#LeporatiZFM07