@article{AA_1997_9_6_a2,
     author = {M. Sh. Birman},
     title = {The discrete spectrum in gaps of the perturbed periodic {Schr\"odinger} {operator.~II.} {Nonregular} perturbations},
     journal = {Algebra i analiz},
     pages = {62--89},
     publisher = {mathdoc},
     volume = {9},
     number = {6},
     year = {1997},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AA_1997_9_6_a2/}
}