@article{DE_1985_21_4_a23,
     author = {V. I. Filippenko},
     title = {Some criteria for discreteness of the negative part of the spectrum of a linear differential operator},
     journal = {Differencialʹnye uravneni\^a},
     pages = {728--731},
     publisher = {mathdoc},
     volume = {21},
     number = {4},
     year = {1985},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1985_21_4_a23/}
}