@article{DE_1968_4_9_a7,
     author = {V. A. Lunkevich},
     title = {The problem of the center for differential equations with discontinuous right-hand sides},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1625--1639},
     publisher = {mathdoc},
     volume = {4},
     number = {9},
     year = {1968},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1968_4_9_a7/}
}