@article{DAN_1963_148_3_a7,
     author = {A. Yu. Levin},
     title = {Some questions on the oscillation of solutions of linear differential equations},
     journal = {Doklady Akademii Nauk},
     pages = {512--515},
     publisher = {mathdoc},
     volume = {148},
     number = {3},
     year = {1963},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1963_148_3_a7/}
}