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@article{MZM_1991_49_6_a6, author = {N. M. Isakov}, title = {$C^r$-property and approximately differentiable functions}, journal = {Matemati\v{c}eskie zametki}, pages = {59--62}, publisher = {mathdoc}, volume = {49}, number = {6}, year = {1991}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/MZM_1991_49_6_a6/} }
N. M. Isakov. $C^r$-property and approximately differentiable functions. Matematičeskie zametki, Tome 49 (1991) no. 6, pp. 59-62. http://geodesic.mathdoc.fr/item/MZM_1991_49_6_a6/