@article{SM_1976_29_2_a5,
     author = {P. R. Popivanov},
     title = {Local solvability of pseudodifferential operators with characteristics of second multiplicity},
     journal = {Sbornik. Mathematics},
     pages = {193--216},
     publisher = {mathdoc},
     volume = {29},
     number = {2},
     year = {1976},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1976_29_2_a5/}
}