@article{DE_1977_13_12_a0,
     author = {Kh. A. Abduvaitov and \`E. M. Muhamadiev},
     title = {Invertibility conditions for a second order differential operator},
     journal = {Differencialʹnye uravneni\^a},
     pages = {2115--2123},
     publisher = {mathdoc},
     volume = {13},
     number = {12},
     year = {1977},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1977_13_12_a0/}
}