@article{DAN_1961_138_4_a6,
     author = {N. P. Kuptsov},
     title = {Conditions for non-selfadjointness of a second-order linear differential operator},
     journal = {Doklady Akademii Nauk},
     pages = {767--770},
     publisher = {mathdoc},
     volume = {138},
     number = {4},
     year = {1961},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1961_138_4_a6/}
}