@Article{TS89,
    Author       = "Trybulec, A. and Swieczkowska, H.",
    Year         = "1989",
    Title        = "{Boolean Properties of Sets}",
    Journal      = "Journal of Formalized Mathematics",
    Volume       = "1",
    Number       = "1",
    Pages        = "17-23",
    Comment      = "TPTPRef"
}