@misc{ elkan03using,
  author = "C. Elkan",
  title = "Using the triangle inequality to accelerate kMeans",
  text = "C. Elkan. Using the triangle inequality to accelerate kMeans. In Proceedings
    of the Twentieth International Conference on Machine Learning, 2003, pp.
    147-153.",
  year = "2003",
  url = "citeseer.ist.psu.edu/elkan03using.html" 
}