Abstract
We prove that the set of all functions in $C[0,1]$, with countably many points at which the derivative does not exist, is ${\pmb \Pi}^1_1$--complete, in particular non--Borel. We obtain the classical Mazurkiewicz's theorem and the recent result of Sofronidis as corollaries from our result.
Citation
Szymon Głb. "On the Complexity of Continuous Functions Differentiable on Cocountable Sets." Real Anal. Exchange 34 (2) 521 - 530, 2008/2009.
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