@article{DAN_1982_266_3_a11,
     author = {P. R. Popivanov},
     title = {Hypoellipticity of differential operators in the class of generalized periodic functions},
     journal = {Doklady Akademii Nauk},
     pages = {565--568},
     publisher = {mathdoc},
     volume = {266},
     number = {3},
     year = {1982},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1982_266_3_a11/}
}