(a) When is a subset of a topological space said to be closed? (b) Fotmulate the definition of topology in terms of closed sets. (c) Suppose (X, 7) is a tôpological space. Use the definition in (b) above to show tha i. Union of any collection of sets in r is an element in 7. ii. The intersection of any finite number of sets in r is an element in 7,

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