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@article{MZM_1987_42_2_a3, author = {S. I. Novikov}, title = {Widths of a class of periodic functions defined by a differential operator}, journal = {Matemati\v{c}eskie zametki}, pages = {194--206}, publisher = {mathdoc}, volume = {42}, number = {2}, year = {1987}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/MZM_1987_42_2_a3/} }
S. I. Novikov. Widths of a class of periodic functions defined by a differential operator. Matematičeskie zametki, Tome 42 (1987) no. 2, pp. 194-206. http://geodesic.mathdoc.fr/item/MZM_1987_42_2_a3/