@article{
    NR94:jancl,
    author = {Niemel{\"a}, Ilkka and Rintanen, Jussi},
    title = "On the impact of stratification on the complexity of nonmonotonic reasoning",
    journal = "Journal of Applied Non-Classical Logics",
    number = "2",
    volume = "4",
    year = "1994",
    pages = "141--179"
}