The family $\mathcal F$ of <closed sets> contains $\varnothing$ and $X$, is closed under arbitrary <intersection>, and is closed under finite <union>. Conversely these axioms define a <topology> by declaring the complements of the members of $\mathcal F$ to be the <open sets>.

Solution

Past exam of the options I course of the University of Oxford / 2009 / E / E1 / a / i / Solution

 Solution (source code)