Ryoso Hamane Toshiya Itoh Improved Approximation Algorithms for Item Pricing with Bounded Degree and Valuation. 187-199 2008 91-D IEICE Trans. Inf. Syst. 2 https://doi.org/10.1093/ietisy/e91-d.2.187 db/journals/ieicet/ieicet91d.html#HamaneI08