Takayuki Ito Hiromitsu Hattori Mark Klein Multi-issue Negotiation Protocol for Agents: Exploring Nonlinear Utility Spaces. 1347-1352 2007 conf/ijcai/2007 IJCAI http://dli.iiit.ac.in/ijcai/IJCAI-2007/PDF/IJCAI07-217.pdf db/conf/ijcai/ijcai2007.html#ItoHK07