@article{DAN_1961_137_2_a5,
     author = {V. A. Il'in},
     title = {A system of classical eigenfunctions of a linear self-adjoint elliptic operator with discontinuous coefficients},
     journal = {Doklady Akademii Nauk},
     pages = {272--275},
     publisher = {mathdoc},
     volume = {137},
     number = {2},
     year = {1961},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1961_137_2_a5/}
}