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@article{MZM_1992_52_2_a5, author = {N. A. Il'yasov}, title = {An inverse theorem of approximation theory of periodic functions in various metrics}, journal = {Matemati\v{c}eskie zametki}, pages = {53--61}, publisher = {mathdoc}, volume = {52}, number = {2}, year = {1992}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/MZM_1992_52_2_a5/} }
N. A. Il'yasov. An inverse theorem of approximation theory of periodic functions in various metrics. Matematičeskie zametki, Tome 52 (1992) no. 2, pp. 53-61. http://geodesic.mathdoc.fr/item/MZM_1992_52_2_a5/