@article{TM_1988_179_a5,
     author = {E. M. Il'in},
     title = {Scattering by unbounded obstacles for second-order elliptic operators},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {80--101},
     year = {1988},
     volume = {179},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TM_1988_179_a5/}
}