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Exercise 4.11. For each of the following, state whether it is true or false. If true,...

Exercise 4.11. For each of the following, state whether it is true or false. If true, prove. If false, provide a counterexample.

(i) Let X and Y be sets from Rn. If X ⊂ Y then X 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 either X or Y is closed and convex (one or the other).

(iii) Let X be an open set and Y ⊆ X. If Y ≠ ∅, then Y is a convex set.

(iv) Suppose X is an open set and Y is a convex set. If X ∩ Y ⊂ X then X ∪ Y is open.

(v) If A and B are closed sets, and A ∩ B = ∅ then A ∪ B is a closed set.

(vi) If a set A is closed, then A cannot be open.

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