Andris Ambainis Martin Beaudry Marats Golovkins Arnolds Kikusts Mark Mercer Denis Thérien Algebraic Results on Quantum Automata. 93-104 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2996&spage=93 2004 conf/stacs/2004 STACS db/conf/stacs/stacs2004.html#AmbainisBGKMT04