@article{SM_1969_9_2_a3,
     author = {S. N. Roze},
     title = {On~the spectrum of an elliptic operator of second order},
     journal = {Sbornik. Mathematics},
     pages = {183--197},
     publisher = {mathdoc},
     volume = {9},
     number = {2},
     year = {1969},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1969_9_2_a3/}
}