@inproceedings{WhyHigher,
  title = "Why higher order constraints are necessary to model frequency assignment problems",
  author = "P.G.Jeavons and N.W.Dunkin and J.E.Bater",
  year = "1998",
  booktitle = "ECAI'98 Workshop on Non-binary constraints",
  url = "ftp://ftp.cs.rhul.ac.uk/pub/constraints/ecaiversion.ps",
}