@article{IM2_2018_82_6_a0,
     author = {L. A. Beklaryan},
     title = {A new approach to the question of existence of periodic solutions
},
     journal = {Izvestiya. Mathematics },
     pages = {1077--1107},
     publisher = {mathdoc},
     volume = {82},
     number = {6},
     year = {2018},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_2018_82_6_a0/}
}