Divyakant Agrawal Ömer Egecioglu Amr El Abbadi Billiard Quorums on the Grid. 9-16 1997 64 Inf. Process. Lett. 1 db/journals/ipl/ipl64.html#AgrawalEA97 http://dx.doi.org/10.1016/S0020-0190(97)00145-2