@article{DAN_1973_209_4_a4,
     author = {Yu. V. Egorov and P. R. Popivanov},
     title = {A class of pseudodifferential equations of principal type having no solutions},
     journal = {Doklady Akademii Nauk},
     pages = {775--777},
     publisher = {mathdoc},
     volume = {209},
     number = {4},
     year = {1973},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1973_209_4_a4/}
}