@article{IM2_2008_72_4_a2,
     author = {D. I. Borisov and R. R. Gadyl'shin},
     title = {On the spectrum of a~periodic operator with a~small localized perturbation},
     journal = {Izvestiya. Mathematics},
     pages = {659--688},
     year = {2008},
     volume = {72},
     number = {4},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_2008_72_4_a2/}
}