@article{TIMM_2014_20_2_a21,
     author = {E. G. Pytkeev and A. G. Chentsov},
     title = {On the structure of ultrafilters and properties related to convergence in topological spaces},
     journal = {Trudy Instituta matematiki i mehaniki},
     pages = {250--267},
     publisher = {mathdoc},
     volume = {20},
     number = {2},
     year = {2014},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TIMM_2014_20_2_a21/}
}