Andris Ambainis Martin Beaudry Marats Golovkins Arnolds Kikusts Mark Mercer Denis Thérien Algebraic Results on Quantum Automata. 165-188 2006 39 Theory Comput. Syst. 1 http://dx.doi.org/10.1007/s00224-005-1263-x db/journals/mst/mst39.html#AmbainisBGKMT06