Paper 1, Section II, F

Analysis II
Part IB, 2014

Define what it means for two norms on a real vector space VV to be Lipschitz equivalent. Show that if two norms on VV are Lipschitz equivalent and FVF \subset V, then FF is closed in one norm if and only if FF is closed in the other norm.

Show that if VV is finite-dimensional, then any two norms on VV are Lipschitz equivalent.

Show that f1=01f(x)dx\|f\|_{1}=\int_{0}^{1}|f(x)| d x is a norm on the space C[0,1]C[0,1] of continuous realvalued functions on [0,1][0,1]. Is the set S={fC[0,1]:f(1/2)=0}S=\{f \in C[0,1]: f(1 / 2)=0\} closed in the norm 1\|\cdot\| 1 ?

Determine whether or not the norm 1\|\cdot\|_{1} is Lipschitz equivalent to the uniform norm\operatorname{norm}\|\cdot\|_{\infty} on C[0,1]C[0,1].

[You may assume the Bolzano-Weierstrass theorem for sequences in Rn\mathbb{R}^{n}.]