@article{MAT_1958_2_2_a3,
     author = {L. Flatto and N. Levins{\cyro}n},
     title = {Periodic solutions of singularly perturbed systems},
     journal = {Matematika},
     pages = {61--68},
     publisher = {mathdoc},
     volume = {2},
     number = {2},
     year = {1958},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MAT_1958_2_2_a3/}
}