Moses Charikar Konstantin Makarychev Yury Makarychev On the Advantage over Random for Maximum Acyclic Subgraph. 625-633 2007 FOCS http://doi.ieeecomputersociety.org/10.1109/FOCS.2007.47 conf/focs/2007 db/conf/focs/focs2007.html#CharikarMM07