Paper 3, Section II, F

Linear Analysis | Part II, 2017

Let KK be a non-empty compact Hausdorff space and let C(K)C(K) be the space of real-valued continuous functions on KK.

(i) State the real version of the Stone-Weierstrass theorem.

(ii) Let AA be a closed subalgebra of C(K)C(K). Prove that f∈Af \in A and g∈Ag \in A implies that m∈Am \in A where the function m:K→Rm: K \rightarrow \mathbb{R} is defined by m(x)=max⁡{f(x),g(x)}m(x)=\max \{f(x), g(x)\}. [You may use without proof that f∈Af \in A implies ∣f∣∈A|f| \in A.]

(iii) Prove that KK is normal and state Urysohn's Lemma.

(iv) For any x∈Kx \in K, define δx∈C(K)∗\delta_{x} \in C(K)^{*} by δx(f)=f(x)\delta_{x}(f)=f(x) for f∈C(K)f \in C(K). Justifying your answer carefully, find

inf⁡x≠y∥δx−δy∥.\inf _{x \neq y}\left\|\delta_{x}-\delta_{y}\right\| .

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