@article{SM_1975_26_4_a4,
     author = {V. A. Marchenko and I. V. Ostrovskii},
     title = {A~characterization of the spectrum of {Hill's} operator},
     journal = {Sbornik. Mathematics},
     pages = {493--554},
     publisher = {mathdoc},
     volume = {26},
     number = {4},
     year = {1975},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1975_26_4_a4/}
}