@article{MZM_1991_49_2_a19,
     author = {Nguyen Minh Tri},
     title = {Global hypoellipticity property of a differential operator},
     journal = {Matemati\v{c}eskie zametki},
     pages = {147--150},
     publisher = {mathdoc},
     volume = {49},
     number = {2},
     year = {1991},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1991_49_2_a19/}
}