Fabio Burderi Antonio Restivo Varieties of Codes and Kraft Inequality. 545-556 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3404&spage=545 2005 conf/stacs/2005 STACS db/conf/stacs/stacs2005.html#BurderiR05