@article{CMFD_2021_67_3_a8,
     author = {G. V. Demidenko and A. V. Dulepova},
     title = {On periodic solutions of one second-order differential equation},
     journal = {Contemporary Mathematics. Fundamental Directions},
     pages = {535--548},
     publisher = {mathdoc},
     volume = {67},
     number = {3},
     year = {2021},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/CMFD_2021_67_3_a8/}
}