@article{DAN_1965_165_6_a7,
     author = {\`E. M. Saak},
     title = {Approximation theorems for differential equations},
     journal = {Doklady Akademii Nauk},
     pages = {1249--1252},
     publisher = {mathdoc},
     volume = {165},
     number = {6},
     year = {1965},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1965_165_6_a7/}
}