@article{DAN_1991_318_1_a0,
     author = {A. V. Aizenshtat and Yu. I. Karlovich and G. S. Litvinchuk},
     title = {Defect numbers of the {D.} {Kveselava{\textendash}N.} {Vekua} operator with a},
     journal = {Doklady Akademii Nauk},
     pages = {11--16},
     year = {1991},
     volume = {318},
     number = {1},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1991_318_1_a0/}
}