@article{CMUC_1982__23_4_a12,
     author = {Butkovi\v{c}ov\'a, Eva},
     title = {Ultrafilters without immediate predecessors in {Rudin-Frol{\'\i}k} order},
     journal = {Commentationes Mathematicae Universitatis Carolinae},
     pages = {757--766},
     publisher = {mathdoc},
     volume = {23},
     number = {4},
     year = {1982},
     mrnumber = {687570},
     zbl = {0507.03020},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMUC_1982__23_4_a12/}
}