@techreport{RR-06-06,
  title = "Generalising Submodularity and Horn Clauses: Tractable optimization problems defined by tournament pair multimorphisms",
  author = "Peter Jeavons and Martin C Cooper and David A Cohen",
  year = "2006",
  institution = "Oxford University Computing Laboratory",
  month = "December",
  number = "RR-06-06",
}