@article{ZNSL_1981_117_a12,
     author = {S. V. Petras},
     title = {On a perturbation of the poles of scattering matrix for varying baundary condition},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {183--191},
     publisher = {mathdoc},
     volume = {117},
     year = {1981},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_1981_117_a12/}
}