Venkatesan Guruswami Sanjeev Khanna Rajmohan Rajaraman F. Bruce Shepherd Mihalis Yannakakis Near-Optimal Hardness Results and Approximation Algorithms for Edge-Disjoint Paths and Related Problems. 19-28 1999 STOC http://doi.acm.org/10.1145/301250.301262 db/conf/stoc/stoc1999.html#GuruswamiKRSY99