Lujun Jia Guolong Lin Guevara Noubir Rajmohan Rajaraman Ravi Sundaram Universal approximations for TSP, Steiner tree, and set cover. 386-395 2005 conf/stoc/2005 STOC http://doi.acm.org/10.1145/1060590.1060649 db/conf/stoc/stoc2005.html#JiaLNRS05