Ioannis Chatzigiannakis Othon Michail Paul G. Spirakis Brief Announcement: Decidable Graph Languages by Mediated Population Protocols. 239-240 2009 DISC http://dx.doi.org/10.1007/978-3-642-04355-0_24 conf/wdag/2009 db/conf/wdag/disc2009.html#ChatzigiannakisMS09