@article{DAN_1967_172_4_a12,
     author = {A. N. Filatov},
     title = {Averaging in systems of differential equations, unsolvable with respect to the derivative},
     journal = {Doklady Akademii Nauk},
     pages = {795--797},
     publisher = {mathdoc},
     volume = {172},
     number = {4},
     year = {1967},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1967_172_4_a12/}
}