@article{DAN_1960_135_4_a4,
     author = {A. Yu. Levin},
     title = {A comparison principle for second-order differential equations},
     journal = {Doklady Akademii Nauk},
     pages = {783--786},
     publisher = {mathdoc},
     volume = {135},
     number = {4},
     year = {1960},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1960_135_4_a4/}
}