@unpublished{
    Niemela99:esslli,
    author = {Niemel{\"a}, Ilkka},
    note = "Lecture notes for a course given at the 11th European Summer School in Logic, Language and Information, Utrecht University, Aug 16--20, 1999. 25 pages.",
    url = "http://www.tcs.hut.fi/~ini/",
    year = "1999",
    month = "",
    title = "Automating Default Reasoning"
}