@article{ZNSL_1981_117_a13,
     author = {S. V. Sukhinin},
     title = {On descreteness of scattering eigenfrequences of periodic cascade},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {192--196},
     publisher = {mathdoc},
     volume = {117},
     year = {1981},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_1981_117_a13/}
}