@techreport{AlgebraicStructures,
  title = "Algebraic structures in combinatorial problems",
  author = "Andrei Bulatov and Peter Jeavons",
  year = "2001",
  institution = "Technische Universitat Dresden",
  number = "MATH-AL-4-2001",
  pages = "32",
  url = "http://www.cs.sfu.ca/~abulatov/papers/varieties.ps",
}