@article{SM_1986_54_2_a1,
     author = {L. I. Kamynin},
     title = {A~theorem on the internal derivative for a~weakly degenerate second-order elliptic equation},
     journal = {Sbornik. Mathematics},
     pages = {297--316},
     publisher = {mathdoc},
     volume = {54},
     number = {2},
     year = {1986},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1986_54_2_a1/}
}