@article{SM_1991_69_2_a0,
     author = {S. A. Nazarov},
     title = {The two terms asymptotics of the solutions of spectral problems with singular perturbations},
     journal = {Sbornik. Mathematics},
     pages = {307--340},
     publisher = {mathdoc},
     volume = {69},
     number = {2},
     year = {1991},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1991_69_2_a0/}
}