@article{PIM_1968_N_S_08_22_a14,
     author = {Brian Warrack and Somashekhar Naimpally},
     title = {Clusters {And} {Ultrafilters}},
     journal = {Publications de l'Institut Math\'ematique},
     pages = {100 },
     publisher = {mathdoc},
     volume = {_N_S_08},
     number = {22},
     year = {1968},
     url = {http://geodesic.mathdoc.fr/item/PIM_1968_N_S_08_22_a14/}
}