@article{Hoare75a,
  title = "Matrix Reduction---an Efficient Method (School Timetables)",
  author = "C.A.R. Hoare and H.C. Johnston",
  year = "1975",
  journal = "Communications of the ACM",
  month = "March",
  number = "3",
  pages = "141--150",
  volume = "18",
}