@article{FAA_1991_25_2_a18,
     author = {M. Sh. Birman},
     title = {The discrete spectrum in the gaps of a second-order perturbed periodic operator},
     journal = {Funkcionalʹnyj analiz i ego prilo\v{z}eni\^a},
     pages = {89--92},
     publisher = {mathdoc},
     volume = {25},
     number = {2},
     year = {1991},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/FAA_1991_25_2_a18/}
}