Julia Kempe Hirotada Kobayashi Keiji Matsumoto Ben Toner Thomas Vidick Entangled Games are Hard to Approximate. 447-456 2008 FOCS http://dx.doi.org/10.1109/FOCS.2008.8 conf/focs/2008 db/conf/focs/focs2008.html#KempeKMTV08