Give examples to show that the finiteness of the collections in parts c and d is essential.
c) for any finite collection G1, G2, ...., Gn of open sets, intersection (at the top of the intersection sign is n and at the bottom is i=1) of Gi is open.
d) For any finite collection F1, F2, ...., Fn of closed sets, union sign (with n at the top of the sign and i=1 at the bottom) of Fi is closed.
Finiteness of sets is investigated. The solution is detailed and well presented.