@article{TMF_1975_25_3_a12,
     author = {A. L. Kitanin},
     title = {Nonstationary perturbation theory for a degenerate discrete level},
     journal = {Teoreti\v{c}eska\^a i matemati\v{c}eska\^a fizika},
     pages = {414--418},
     year = {1975},
     volume = {25},
     number = {3},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TMF_1975_25_3_a12/}
}