@article{DAN_1957_112_5_a5,
     author = {A. I. Koshelev},
     title = {On the differentiability of solutions of elliptical differential equations},
     journal = {Doklady Akademii Nauk},
     pages = {806--809},
     year = {1957},
     volume = {112},
     number = {5},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1957_112_5_a5/}
}