@article{INTO_2020_185_a1,
     author = {V. V. Abramov and E. Yu. Liskina},
     title = {On periodic solutions of a second-order ordinary differential equation},
     journal = {Itogi nauki i tehniki. Sovremenna\^a matematika i e\"e prilo\v{z}eni\^a. Temati\v{c}eskie obzory},
     pages = {13--18},
     publisher = {mathdoc},
     volume = {185},
     year = {2020},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/INTO_2020_185_a1/}
}