@article{AA_1997_9_1_a5,
     author = {O. L. Safronov},
     title = {Emergence and disappearance of the discrete spectrum in a gap of a second-order periodic operator under decreasing perturbations with alternating signs},
     journal = {Algebra i analiz},
     pages = {148--166},
     publisher = {mathdoc},
     volume = {9},
     number = {1},
     year = {1997},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AA_1997_9_1_a5/}
}