@article{IVM_1972_8_a7,
     author = {Z. I. Kozlova},
     title = {$Z_N$-classification, and approximation of sets},
     journal = {Izvesti\^a vys\v{s}ih u\v{c}ebnyh zavedenij. Matematika},
     pages = {60--69},
     year = {1972},
     number = {8},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/IVM_1972_8_a7/}
}