@article{MASLO_1974_24_2_a7,
     author = {Jakub{\'\i}k, J\'an},
     title = {Quasiorder on {Systems} of {Directed} {Sets}},
     journal = {Mathematica slovaca},
     pages = {173--177},
     year = {1974},
     volume = {24},
     number = {2},
     mrnumber = {0351925},
     zbl = {0281.06003},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/MASLO_1974_24_2_a7/}
}