Gus Gutoski John Watrous Quantum Interactive Proofs with Competing Provers. 605-616 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3404&spage=605 2005 conf/stacs/2005 STACS db/conf/stacs/stacs2005.html#GutoskiW05