Exercise 4.11. For each of the following, state whether it is true or false. If true, prove. If false, provide a counterexample.
(i) LetX andY besetsfromRn. IfX⊂Y thenX is closed if and only if Y is closed.
(ii) Let X and Y be sets from Rn. If X ∩Y is closed and convex then eitherX or Y is closed and convex (one or the other).
(iii) LetX beanopensetandY ⊆X. IfY ≠∅,thenY isaconvexset.
(iv) SupposeX isanopensetandY isaconvexset. IfX∩Y ⊂X then
X∪Y is open.
(v) If AandB are closed sets,and A∩B=∅ then A∪B is a closed set.
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