@article{SM_1975_26_4_a2,
     author = {N. A. Shananin},
     title = {On local solvability of equations of quasi-principal type},
     journal = {Sbornik. Mathematics},
     pages = {458--470},
     publisher = {mathdoc},
     volume = {26},
     number = {4},
     year = {1975},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1975_26_4_a2/}
}