@article{MZM_1989_46_6_a17,
     author = {O. A. Timoshin},
     title = {A criterion for finiteness of best approximation of a differential polynomial},
     journal = {Matemati\v{c}eskie zametki},
     pages = {114--116},
     publisher = {mathdoc},
     volume = {46},
     number = {6},
     year = {1989},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1989_46_6_a17/}
}