Grant Schoenebeck Luca Trevisan Madhur Tulsiani Tight integrality gaps for Lovasz-Schrijver LP relaxations of vertex cover and max cut. 302-310 2007 conf/stoc/2007 STOC http://doi.acm.org/10.1145/1250790.1250836 db/conf/stoc/stoc2007.html#SchoenebeckTT07