Extending Peano derivatives: necessary and sufficient conditions
Hans Volkmer (1999)
Fundamenta Mathematicae
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The paper treats functions which are defined on closed subsets of [0,1] and which are k times Peano differentiable. A necessary and sufficient condition is given for the existence of a k times Peano differentiable extension of such a function to [0,1]. Several applications of the result are presented. In particular, functions defined on symmetric perfect sets are studied.