Jurek Czyzowicz Leszek Gasieniec Andrzej Pelc Gathering few fat mobile robots in the plane. 481-499 2009 410 Theor. Comput. Sci. 6-7 http://dx.doi.org/10.1016/j.tcs.2008.10.005 db/journals/tcs/tcs410.html#CzyzowiczGP09