@article{TM_1987_180_a141,
     author = {V. V. Shan'kov},
     title = {Difference operators with variable step},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {229--230},
     year = {1987},
     volume = {180},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TM_1987_180_a141/}
}