R. N. Uma Joel Wein David P. Williamson On the relationship between combinatorial and LP-based lower bounds for NP-hard scheduling problems. 241-256 2006 361 Theor. Comput. Sci. 2-3 http://dx.doi.org/10.1016/j.tcs.2006.05.013 db/journals/tcs/tcs361.html#UmaWW06