@article{MZM_1973_13_4_a1,
     author = {V. N. Rusak},
     title = {Estimates of the derivative of a~rational function},
     journal = {Matemati\v{c}eskie zametki},
     pages = {493--498},
     publisher = {mathdoc},
     volume = {13},
     number = {4},
     year = {1973},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1973_13_4_a1/}
}