Anupam Gupta Amit Kumar Martin Pál Tim Roughgarden Approximation Via Cost-Sharing: A Simple Approximation Algorithm for the Multicommodity Rent-or-Buy Problem. 606-615 2003 conf/focs/2003 FOCS http://doi.ieeecomputersociety.org/10.1109/SFCS.2003.1238233 db/conf/focs/focs2003.html#GuptaKPR03