@article{DE_1968_4_6_a15,
     author = {Yu. K. Lando},
     title = {The index and the normal solvability of integro-differential operators},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1112--1126},
     publisher = {mathdoc},
     volume = {4},
     number = {6},
     year = {1968},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1968_4_6_a15/}
}