André Berthiaume Todd Bittner Ljubomir Perkovic Amber Settle Janos Simon Bounding the firing synchronization problem on a ring. 213-228 2004 320 Theor. Comput. Sci. 2-3 http://dx.doi.org/10.1016/j.tcs.2004.01.036 db/journals/tcs/tcs320.html#BerthiaumeBPSS04