Corina Cîrstea Alexander Kurz Dirk Pattinson Lutz Schröder Yde Venema Modal Logics are Coalgebraic. 128-140 2008 BCS Int. Acad. Conf. http://www.bcs.org/server.php?show=ConWebDoc.22873 conf/bcs/2008 db/conf/bcs/bcs2008.html#CirsteaKPSV08