@article{ADM_2015_19_2_a8,
     author = {O. V. Petrenko and I. V. Protasov},
     title = {Ultrafilters on $G$-spaces},
     journal = {Algebra and discrete mathematics},
     pages = {254--269},
     publisher = {mathdoc},
     volume = {19},
     number = {2},
     year = {2015},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/ADM_2015_19_2_a8/}
}