Hiroshi Umeo Jean-Baptiste Yunès Naoki Kamikawa About 4-States Solutions to the Firing Squad Synchronization Problem. 108-113 2008 ACRI http://dx.doi.org/10.1007/978-3-540-79992-4_14 conf/acri/2008 db/conf/acri/acri2008.html#UmeoYK08