Kevin Leyton-Brown Eugene Nudelman Yoav Shoham Learning the Empirical Hardness of Optimization Problems: The Case of Combinatorial Auctions. 556-572 2002 conf/cp/2002 CP http://link.springer.de/link/service/series/0558/bibs/2470/24700556.htm db/conf/cp/cp2002.html#Leyton-BrownNS02