@article{MZM_1989_45_2_a1,
     author = {N. V. Velichko},
     title = {Ultrasequential spaces},
     journal = {Matemati\v{c}eskie zametki},
     pages = {15--21},
     publisher = {mathdoc},
     volume = {45},
     number = {2},
     year = {1989},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1989_45_2_a1/}
}