@article{DE_1997_33_1_a5,
     author = {V. A. Gorelov},
     title = {On the change of a finite number of elements in a system of root functions of a differential operator without loss of the basis property},
     journal = {Differencialʹnye uravneni\^a},
     pages = {33--38},
     publisher = {mathdoc},
     volume = {33},
     number = {1},
     year = {1997},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1997_33_1_a5/}
}