@article{DE_1987_23_12_a3,
     author = {G. A. Leonov},
     title = {A frequency criterion for the existence of limit cycles of dynamical systems with a cylindrical phase space},
     journal = {Differencialʹnye uravneni\^a},
     pages = {2047--2051},
     publisher = {mathdoc},
     volume = {23},
     number = {12},
     year = {1987},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1987_23_12_a3/}
}