@article{MZM_1967_2_5_a10,
     author = {M. G. Gasymov and V. V. Zhikov and B. M. Levitan},
     title = {Conditions for discreteness and finiteness of the negative spectrum of {Schr\"odinger's} operator equation},
     journal = {Matemati\v{c}eskie zametki},
     pages = {531--538},
     publisher = {mathdoc},
     volume = {2},
     number = {5},
     year = {1967},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1967_2_5_a10/}
}