The Hausdorff problem
Matematičeskie zametki, Tome 14 (1973) no. 2, pp. 197-200
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It is proved that if the set of points of discontinuity of a real and everywhere symmetrically continuous function $f(x)$, $x\in(a,b)$, is closed, then it is not more than countable.
@article{MZM_1973_14_2_a3,
author = {S. P. Ponomarev},
title = {The {Hausdorff} problem},
journal = {Matemati\v{c}eskie zametki},
pages = {197--200},
year = {1973},
volume = {14},
number = {2},
language = {ru},
url = {http://geodesic.mathdoc.fr/item/MZM_1973_14_2_a3/}
}
S. P. Ponomarev. The Hausdorff problem. Matematičeskie zametki, Tome 14 (1973) no. 2, pp. 197-200. http://geodesic.mathdoc.fr/item/MZM_1973_14_2_a3/