@phdthesis{
    Janhunen98:thesis,
    author = "Janhunen, Tomi",
    month = "March",
    url = "http://www.tcs.hut.fi/Publications/series-a.shtml",
    school = "Helsinki University of Technology, Department of Computer Science and Engineering",
    year = "1998",
    title = "Non-Monotonic Systems: A Framework for Analyzing Semantics and Structural Properties of Non-Monotonic Reasoning"
}