Rajiv Gandhi Magnús M. Halldórsson Guy Kortsarz Hadas Shachnai Improved bounds for scheduling conflicting jobs with minsum criteria. 2008 4 ACM Transactions on Algorithms 1 http://doi.acm.org/10.1145/1328911.1328922 db/journals/talg/talg4.html#GandhiHKS08