Dimitry S. Ananichev Alessandra Cherubini Mikhail V. Volkov An Inverse Automata Algorithm for Recognizing 2-Collapsing Words. 270-282 http://dx.doi.org/10.1007/3-540-45005-X_23 2002 conf/dlt/2002 Developments in Language Theory db/conf/dlt/dlt2002.html#AnanichevCV02