@article{DAN_1969_185_1_a0,
     author = {Yu. N. Bibikov},
     title = {The existence of invariant tori in the neighborhodd of a state of equilbrium of a system of differential equations},
     journal = {Doklady Akademii Nauk},
     pages = {9--12},
     publisher = {mathdoc},
     volume = {185},
     number = {1},
     year = {1969},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1969_185_1_a0/}
}