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 F⊂VF \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 ∥f∥1=∫01∣f(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={f∈C[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}.]

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