Hellis Tamm Matti Nykänen Esko Ukkonen Size Reduction of Multitape Automata. 329-330 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3317&spage=329 2004 conf/wia/2004 CIAA db/conf/wia/ciaa2004.html#TammNU04