@Article{Mar97-JFM,
    Author       = "Marasik, A.",
    Year         = "1997",
    Title        = "{Algebraic Operation on Subsets of Many Sorted Sets}",
    Journal      = "Journal of Formalized Mathematics",
    Volume       = "6",
    Number       = "3",
    Pages        = "397-401",
    Comment      = "TPTPRef,CLOSURE3"
}