Josh Buresh-Oppenheim Tsuyoshi Morioka Relativized NP Search Problems and Propositional Proof Systems. 54-67 2004 conf/coco/2004 IEEE Conference on Computational Complexity http://csdl.computer.org/comp/proceedings/ccc/2004/2120/00/21200054abs.htm db/conf/coco/coco2004.html#Buresh-OppenheimM04