Paper 3, Section II, I

Topics in Analysis | Part II, 2015

Let α>0\alpha>0. By considering the set EmE_{m} consisting of those f∈C([0,1])f \in C([0,1]) for which there exists an x∈[0,1]x \in[0,1] with ∣f(x+h)−f(x)∣⩽m∣h∣α|f(x+h)-f(x)| \leqslant m|h|^{\alpha} for all x+h∈[0,1]x+h \in[0,1], or otherwise, give a Baire category proof of the existence of continuous functions ff on [0,1][0,1] such that

lim sup⁡h→0∣h∣−α∣f(x+h)−f(x)∣=∞\limsup _{h \rightarrow 0}|h|^{-\alpha}|f(x+h)-f(x)|=\infty

at each x∈[0,1]x \in[0,1].

Are the following statements true? Give reasons.

(i) There exists an f∈C([0,1])f \in C([0,1]) such that

lim sup⁡h→0∣h∣−α∣f(x+h)−f(x)∣=∞\limsup _{h \rightarrow 0}|h|^{-\alpha}|f(x+h)-f(x)|=\infty

for each x∈[0,1]x \in[0,1] and each α>0\alpha>0.

(ii) There exists an f∈C([0,1])f \in C([0,1]) such that

lim sup⁡h→0∣h∣−α∣f(x+h)−f(x)∣=∞\limsup _{h \rightarrow 0}|h|^{-\alpha}|f(x+h)-f(x)|=\infty

for each x∈[0,1]x \in[0,1] and each α⩾0\alpha \geqslant 0.

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