@article{DE_1969_5_3_a14,
     author = {Yu. K. Lando},
     title = {The $F$-index and $F$-normal solvability of integro-differential operators},
     journal = {Differencialʹnye uravneni\^a},
     pages = {546--555},
     publisher = {mathdoc},
     volume = {5},
     number = {3},
     year = {1969},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1969_5_3_a14/}
}