@article{TRSPY_1990_188_a4,
     author = {Yu. E. Karpeshina},
     title = {Perturbation theory for the {Schr\"odinger} operator with periodic potential},
     journal = {Informatics and Automation},
     pages = {88--116},
     publisher = {mathdoc},
     volume = {188},
     year = {1990},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TRSPY_1990_188_a4/}
}