@article{cjz08:tcs,
  title = "The expressive power of valued constraints: {H}ierarchies and collapses",
  author = "David A. Cohen and Peter G. Jeavons and Stanislav \v{Z}ivn\'y",
  year = "2008",
  journal = "Theoretical Computer Science",
  number = "1",
  pages = "137--153",
  url = "http://zivny.cz/publications/cjz08tcs-preprint.pdf",
  volume = "409",
  doi = "10.1016/j.tcs.2008.08.036",
}