2
Challenge
Given a set T of subsets of a finite set S={1,2,3,...,n}, determine whether T is a topology or not.
Explanation
The powerset P(S) of some set S is the set of all subsets of S. Some examples:
S = {}, P(S) = {{}}
S = {1}, P(S) = {{}, {1}}
S = {1,2}, P(S) = {{}, {1}, {2}, {1,2}
S = {1,...