@article{SM_1969_7_1_a7,
     author = {Yu. V. Egorov and V. A. Kondrat'ev},
     title = {The oblique derivative problem},
     journal = {Sbornik. Mathematics},
     pages = {139--169},
     publisher = {mathdoc},
     volume = {7},
     number = {1},
     year = {1969},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1969_7_1_a7/}
}