@article{ADM_2018_25_2_a7,
     author = {Igor Protasov},
     title = {Some more algebra on ultrafilters in~metric~spaces},
     journal = {Algebra and discrete mathematics},
     pages = {286--293},
     year = {2018},
     volume = {25},
     number = {2},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/ADM_2018_25_2_a7/}
}