@article{SM_1973_19_4_a4,
     author = {O. A. Oleinik and E. V. Radkevich},
     title = {On~the analyticity of solutions of linear partial differential equations},
     journal = {Sbornik. Mathematics},
     pages = {581--596},
     publisher = {mathdoc},
     volume = {19},
     number = {4},
     year = {1973},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1973_19_4_a4/}
}