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 fAf \in A and gAg \in A implies that mAm \in A where the function m:KRm: 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 fAf \in A implies fA|f| \in A.]

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

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

infxyδxδy.\inf _{x \neq y}\left\|\delta_{x}-\delta_{y}\right\| .