@article{MZM_1976_20_5_a7,
     author = {Yu. Ya. Belov},
     title = {Approximation of a~linear system of second-order differential equations},
     journal = {Matemati\v{c}eskie zametki},
     pages = {693--702},
     publisher = {mathdoc},
     volume = {20},
     number = {5},
     year = {1976},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1976_20_5_a7/}
}