@techreport{SurveyTractable,
  title = "A Survey of Tractable Constraint Satisfaction Problems",
  author = "J.K.Pearson and P.G.Jeavons",
  year = "1997",
  institution = "Royal Holloway, University of London",
  month = "July",
  number = "CSD-TR-97-15",
  url = "ftp://ftp.cs.rhul.ac.uk/pub/constraints/survey.ps",
}