The Details: Since definitions vary: A topological space $(X,\tau)$ is a set $\tau$ of subsets of $X$, called closed subsets, such that $\varnothing, X\in\tau$, The intersection $$\bigcap_{i\in I}X_i$$ of any closed subsets $(X_i)_{i\in I}$ is closed, where $I$ is arbitrary, and The union of fi...