Derivatives and closed sets
The author proves that a real function defined on a closed set S and differentiable relative to S can be extended to a function differentiable on the whole real line. This is a generalization of a result of \textit{G. Petruska} and \textit{M. Laczkovich} [Acta. Math. Acad. Sci. Hung. 25, 189- 212 (1974; Zbl 0279.26003)].
extension to a function differentiable on the whole real line
scientific article; zbMATH DE number 3863515