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 fC([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)mhα|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 suph0hαf(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 fC([0,1])f \in C([0,1]) such that

lim suph0hαf(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 fC([0,1])f \in C([0,1]) such that

lim suph0hαf(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 α0\alpha \geqslant 0.