Ioannis Caragiannis Aleksei V. Fishkin Christos Kaklamanis Evi Papaioannou A Tight Bound for Online Coloring of Disk Graphs. 78-88 2005 conf/sirocco/2005 SIROCCO http://dx.doi.org/10.1007/11429647_8 db/conf/sirocco/sirocco2005.html#CaragiannisFKP05