@article{DAN_1969_184_4_a15,
     author = {V. I. Cherepanov},
     title = {The parametrization method in the perturbation theory for systems with $SR$-symmetry},
     journal = {Doklady Akademii Nauk},
     pages = {820--823},
     publisher = {mathdoc},
     volume = {184},
     number = {4},
     year = {1969},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1969_184_4_a15/}
}