Heikki Tauriainen Nested Emptiness Search for Generalized Büchi Automata. 127-154 2006 70 Fundam. Inform. 1-2 http://iospress.metapress.com/openurl.asp?genre=article&issn=0169-2968&volume=70&issue=1&spage=127 db/journals/fuin/fuin70.html#Tauriainen06