@article{MZM_1969_6_5_a7,
     author = {V. N. Gabushin},
     title = {On the best approximation of the differentiation operator on the half-line},
     journal = {Matemati\v{c}eskie zametki},
     pages = {573--582},
     publisher = {mathdoc},
     volume = {6},
     number = {5},
     year = {1969},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1969_6_5_a7/}
}