@article{SM_1976_28_4_a5,
     author = {V. A. Kondrat'ev and S. D. \`Eidel'man},
     title = {On the summability of positive solutions of partial differential equations of arbitrary order in a~neighborhood of a~characteristic manifold},
     journal = {Sbornik. Mathematics},
     pages = {521--531},
     year = {1976},
     volume = {28},
     number = {4},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1976_28_4_a5/}
}