@article{DAN_1958_120_5_a1,
     author = {Yu. S. Bogdanov},
     title = {Some tests for the absence of closed trajectories},
     journal = {Doklady Akademii Nauk},
     pages = {939--940},
     publisher = {mathdoc},
     volume = {120},
     number = {5},
     year = {1958},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1958_120_5_a1/}
}