@misc{zj07:cp-dp,
  title = "Expressibility of valued constraints",
  author = "Stanislav \v{Z}ivn\'y and Peter Jeavons",
  year = "2007",
  booktitle = "{P}roc. of the {D}octoral {P}rogramme of {C}{P}'07",
  month = "September",
  pages = "193--198",
}