@article{DE_1988_24_5_a20,
     author = {A. Yu. Kolesov and Yu. S. Kolesov},
     title = {Construction of the normal form in a neighborhood of a cycle by means of the {Krylov{\textendash}Bogolyubov{\textendash}Mitropol'skiǐ} asymptotic method},
     journal = {Differencialʹnye uravneni\^a},
     pages = {891--894},
     year = {1988},
     volume = {24},
     number = {5},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1988_24_5_a20/}
}