@article{RM_1990_45_4_a7,
     author = {Yu. D. Golovatyj},
     title = {The spectral {Neumann} problem for the {Laplace} operator with a~singularly perturbed density},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {165--167},
     publisher = {mathdoc},
     volume = {45},
     number = {4},
     year = {1990},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/RM_1990_45_4_a7/}
}