Stephen L. Bloom Zoltán Ésik Werner Kuich Cycle-Free Finite Automata in Partial Iterative Semirings. 1-12 2009 CAI http://dx.doi.org/10.1007/978-3-642-03564-7_1 conf/cai/2009 db/conf/cai/cai2009.html#BloomEK09