Jozef Gruska Salvatore La Torre Mimmo Parente The Firing Squad Synchronization Problem on Squares, Toruses and Rings. 637-654 2007 18 Int. J. Found. Comput. Sci. 3 http://dx.doi.org/10.1142/S0129054107004875 db/journals/ijfcs/ijfcs18.html#GruskaTP07