@article{DE_1997_33_1_a19,
     author = {S. R. Umarov and \`E. M. Saidamatov},
     title = {On conditions for the discreteness of the spectrum for a general pseudo-differential operator},
     journal = {Differencialʹnye uravneni\^a},
     pages = {133--135},
     publisher = {mathdoc},
     volume = {33},
     number = {1},
     year = {1997},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1997_33_1_a19/}
}