@unpublished{
    Niemela94:cade,
    author = {Niemel{\"a}, Ilkka and Schwind, Camilla},
    note = "Lecture notes for a tutorial given at the 12th International Conference on Automated Deduction, Nancy, France, June 28--July 1, 1994. 44 pages.",
    url = "http://www.tcs.hut.fi/~ini/",
    year = "1994",
    month = "",
    title = "Proof Systems for Nonmonotonic Logics"
}