@article{DAN_1966_171_4_a3,
     author = {Yu. V. Egorov},
     title = {On pseudo-differential operators of the principal type},
     journal = {Doklady Akademii Nauk},
     pages = {778--780},
     publisher = {mathdoc},
     volume = {171},
     number = {4},
     year = {1966},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1966_171_4_a3/}
}