@article{TMF_1975_24_2_a7,
     author = {A. N. Vasil'ev and A. L. Kitanin},
     title = {Nonstationary perturbation theory for the energy shifts of a~degenerate level},
     journal = {Teoreti\v{c}eska\^a i matemati\v{c}eska\^a fizika},
     pages = {219--229},
     publisher = {mathdoc},
     volume = {24},
     number = {2},
     year = {1975},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TMF_1975_24_2_a7/}
}