Jean-Charles Delvenne Petr Kurka Vincent D. Blondel Computational Universality in Symbolic Dynamical Systems. 104-115 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3354&spage=104 2004 conf/mcu/2004 MCU db/conf/mcu/mcu2004.html#DelvenneKB04