- https://github.com/BalanceYan/TopologicalSpaces/blob/main/Topology.v
- https://github.com/coq-community/topology/blob/master/theories/Topology/TopologicalSpaces.v
- https://coq.inria.fr/library/Coq.Sets.Ensembles.html
- https://coq.inria.fr/library/Coq.Logic.ClassicalChoice.html
- https://coq.inria.fr/library/Coq.Sets.Powerset.html