@article{CMUC_1981__22_4_a4,
     author = {Sochor, Anton{\'\i}n and Vop\v{e}nka, Petr},
     title = {Ultrafilters of sets},
     journal = {Commentationes Mathematicae Universitatis Carolinae},
     pages = {689--699},
     publisher = {mathdoc},
     volume = {22},
     number = {4},
     year = {1981},
     mrnumber = {647017},
     zbl = {0493.03028},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMUC_1981__22_4_a4/}
}