@article{DE_1981_17_11_a15,
     author = {M. A. Amatov},
     title = {Periodic solutions of a nonlinear system},
     journal = {Differencialʹnye uravneni\^a},
     pages = {2084--2085},
     year = {1981},
     volume = {17},
     number = {11},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1981_17_11_a15/}
}