On the points of non-differentiability of convex functions
We characterize sets of non-differentiability points of convex functions on . This completes (in ) the result by Zajíček [2] which gives a characterization of the magnitude of these sets.
A d.c. function need not be difference of convex functions
In [2] a delta convex function on is constructed which is strictly differentiable at but it is not representable as a difference of two convex function of this property. We improve this result by constructing a delta convex function of class which cannot be represented as a difference of two convex functions differentiable at 0. Further we give an example of a delta convex function differentiable everywhere which is not strictly differentiable at 0.
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