@article{DAN_1957_116_4_a10,
     author = {V. F. Tkachev},
     title = {New sufficient conditions for stability, semistability and instability of the limit cycle of the 
},
     journal = {Doklady Akademii Nauk},
     pages = {564--567},
     publisher = {mathdoc},
     volume = {116},
     number = {4},
     year = {1957},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1957_116_4_a10/}
}