@Article{vpv-2007,
  title = 	 {Polyhedral properties of the K-median problem on a tree},
  author = 	 {Sven de Vries and Marc E. Posner and Rakesh V. Vohra},
  journal = 	 {Math. Prog. Ser. A},
  url= {http://dx.doi.org/10.1007/s10107-006-0002-7},
  year = 	 2007,
  volume = 	 110,
  number = 	 2,
  pages = 	 {261--285}}