@article{RM_1999_54_4_a13,
     author = {O. A. Kovaleva},
     title = {On a~property of the index of non-local elliptic problems},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {843--844},
     publisher = {mathdoc},
     volume = {54},
     number = {4},
     year = {1999},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/RM_1999_54_4_a13/}
}