@article{MZM_1973_14_1_a2,
     author = {A. A. Ligun},
     title = {Exact constants of approximation for differentiable periodic functions},
     journal = {Matemati\v{c}eskie zametki},
     pages = {21--30},
     publisher = {mathdoc},
     volume = {14},
     number = {1},
     year = {1973},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1973_14_1_a2/}
}