@article{DAN_1991_321_6_a7,
     author = {A. L. Skubachevskii and G. M. Steblov},
     title = {On the spectrum of differential operators with a domain that is},
     journal = {Doklady Akademii Nauk},
     pages = {1158--1163},
     publisher = {mathdoc},
     volume = {321},
     number = {6},
     year = {1991},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1991_321_6_a7/}
}