@article{VSGU_2010_6_a9,
     author = {O. P. Filatov},
     title = {The theorem of averaging and indeterminate conditional periodic motions},
     journal = {Vestnik Samarskogo universiteta. Estestvennonau\v{c}na\^a seri\^a},
     pages = {87--92},
     publisher = {mathdoc},
     number = {6},
     year = {2010},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/VSGU_2010_6_a9/}
}