@article{TM_1974_131_a8,
     author = {G. G. Kazaryan},
     title = {The comparison of differential operators and differential operators of constant strength},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {94--118},
     year = {1974},
     volume = {131},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TM_1974_131_a8/}
}