Richard Cleve William Slofstra Falk Unger Sarvagya Upadhyay Perfect Parallel Repetition Theorem for Quantum Xor Proof Systems. 282-299 2008 17 Computational Complexity 2 http://dx.doi.org/10.1007/s00037-008-0250-4 db/journals/cc/cc17.html#CleveSUU08