@article{MZM_1988_43_6_a5,
     author = {A. A. Ligun},
     title = {Exact inequalities of {Jackson} type for periodic functions in space $L_2$},
     journal = {Matemati\v{c}eskie zametki},
     pages = {757--769},
     publisher = {mathdoc},
     volume = {43},
     number = {6},
     year = {1988},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1988_43_6_a5/}
}