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@article{MZM_1972_12_4_a15, author = {V. A. Il'in}, title = {Some questions in the spectral theory of elliptic operators}, journal = {Matemati\v{c}eskie zametki}, pages = {489--499}, publisher = {mathdoc}, volume = {12}, number = {4}, year = {1972}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/MZM_1972_12_4_a15/} }
V. A. Il'in. Some questions in the spectral theory of elliptic operators. Matematičeskie zametki, Tome 12 (1972) no. 4, pp. 489-499. http://geodesic.mathdoc.fr/item/MZM_1972_12_4_a15/