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@article{MZM_1967_2_5_a6, author = {Yu. N. Subbotin}, title = {The best approximation of a class of functions by another class}, journal = {Matemati\v{c}eskie zametki}, pages = {495--504}, publisher = {mathdoc}, volume = {2}, number = {5}, year = {1967}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/MZM_1967_2_5_a6/} }
Yu. N. Subbotin. The best approximation of a class of functions by another class. Matematičeskie zametki, Tome 2 (1967) no. 5, pp. 495-504. http://geodesic.mathdoc.fr/item/MZM_1967_2_5_a6/