@article{ClassifyingComplexity,
  title = "Classifying the complexity of constraints using finite algebras",
  author = "Andrei Bulatov and Peter Jeavons and Andrei Krokhin",
  year = "2005",
  journal = "SIAM Journal on Computing",
  number = "34",
  pages = "720-742",
  url = "http://www.comlab.ox.ac.uk/activities/constraints/publications/SIAMclassifying.pdf",
  doi = "10.1137/S0097539700376676",
}