@article{DAN_1970_194_4_a6,
     author = {I. M. Koval'chik},
     title = {Linear equations with functional derivatives},
     journal = {Doklady Akademii Nauk},
     pages = {763--766},
     publisher = {mathdoc},
     volume = {194},
     number = {4},
     year = {1970},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1970_194_4_a6/}
}