@article{IM2_1972_6_2_a5,
     author = {N. P. Korneichuk},
     title = {Inequalities for differentiable periodic functions and best approximation of one class of functions by another},
     journal = {Izvestiya. Mathematics },
     pages = {417--428},
     publisher = {mathdoc},
     volume = {6},
     number = {2},
     year = {1972},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1972_6_2_a5/}
}