César Luis Alonso Fátima Drubi Judith Gómez-García José Luis Montaña Word Equation Systems: The Heuristic Approach. 83-92 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3171&spage=83 2004 conf/sbia/2004 SBIA db/conf/sbia/sbia2004.html#AlonsoDGM04