https://en.wikipedia.org/wiki/Topology https://en.wikipedia.org/wiki/Closed_set https://mathworld.wolfram.com/LimitPoint.html https://mathworld.wolfram.com/BoundedSet.html https://en.wikipedia.org/wiki/Subset https://en.wikipedia.org/wiki/Neighbourhood_(mathematics) https://en.wikipedia.org/wiki/Hausdorff_space https://en.wikipedia.org/wiki/Empty_set#:~:text=In%20mathematics%2C%20the%20empty%20set,its%20existence%20can%20be%20deduced. https://en.wikipedia.org/wiki/Locally_compact_space https://en.wikipedia.org/wiki/Haar_measure https://en.wikipedia.org/wiki/Measure_(mathematics) https://mathworld.wolfram.com/HaarMeasure.html https://mathworld.wolfram.com/Sigma-Algebra.html https://en.wikipedia.org/wiki/%CE%A3-algebra https://en.wikipedia.org/wiki/Borel_set