Martin Bichler Stefan Schneider Kemal Guler Mehmet Sayal Solving Winner Determination Problems for Auctions with Economies of Scope and Scale. 93-94 2009 AMMA http://dx.doi.org/10.1007/978-3-642-03821-1_15 conf/amma/2009 db/conf/amma/amma2009.html#BichlerSGS09