In point-set topology, the properties of the set S are:
- X and ∅ belongs to the set S.
- The intersection of any subsets belongs to the set S.
- The union of any subsets belongs to the set S.
For instance:
Let τ = {X,∅}. Then, it's the topology. We call that the trivial or discrete topology. If the set is indiscrete topology, then it contains infinitely many elements!