@article{DAN_1997_352_4_a6,
     author = {O. M. Penkin},
     title = {On the maximum principle for an elliptic equation on a},
     journal = {Doklady Akademii Nauk},
     pages = {462--465},
     publisher = {mathdoc},
     volume = {352},
     number = {4},
     year = {1997},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1997_352_4_a6/}
}