@inproceedings{Zivny07:cp,
  title = "The expressive power of valued constraints: Hierarchies and collapses",
  author = "David A. Cohen and Peter G. Jeavons and Stanislav \v{Z}ivn\'y",
  year = "2007",
  booktitle = "Proceedings of the 13th International Conference on Principles and Practice of Constraint Programming (CP'07)",
  pages = "798-805",
  series = "Lecture Notes in Computer Science",
  url = "http://zivny.cz/publications/cjz07cp-preprint.pdf",
  volume = "4741",
  doi = "10.1007/978-3-540-74970-7_57",
}