@article{ZNSL_1995_222_a9,
     author = {Yu. G. Shondin},
     title = {Perturbations of elliptic operators on high codimension subsets and the extension theory on an indefinite metric space},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {246--292},
     publisher = {mathdoc},
     volume = {222},
     year = {1995},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_1995_222_a9/}
}