Cyril Allauzen Mehryar Mohri Ashish Rastogi General Algorithms for Testing the Ambiguity of Finite Automata. 108-120 2008 Developments in Language Theory http://dx.doi.org/10.1007/978-3-540-85780-8_8 conf/dlt/2008 db/conf/dlt/dlt2008.html#AllauzenMR08