Yiling Chen Lance Fortnow Nicolas S. Lambert David M. Pennock Jennifer Wortman Complexity of combinatorial market makers. 190-199 2008 ACM Conference on Electronic Commerce http://doi.acm.org/10.1145/1386790.1386822 conf/sigecom/2008 db/conf/sigecom/sigecom2008.html#ChenFLPW08