@article{DE_1970_6_6_a20,
     author = {E. D. Zhitelzeif},
     title = {A test for the existence of a periodic solution of the {Li\'enard} equation},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1127--1130},
     publisher = {mathdoc},
     volume = {6},
     number = {6},
     year = {1970},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1970_6_6_a20/}
}