@article{DAN_1972_203_5_a8,
     author = {S. D. Shchuko},
     title = {On the problem of distinguishing between a center and a focus},
     journal = {Doklady Akademii Nauk},
     pages = {1008--1010},
     publisher = {mathdoc},
     volume = {203},
     number = {5},
     year = {1972},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1972_203_5_a8/}
}