The closure of a set is the smallest closed set containing . Closed sets are closed under arbitrary intersection, so it is also the intersection of all closed sets containing . Typically, it is just with all of its accumulation points.
See alsoClosed Set, Sequence, Set Closure, Topology
This entry contributed by Todd Rowland
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Rowland, Todd. "Topological Closure." From MathWorld--A Wolfram Web Resource, created by Eric W. Weisstein. https://mathworld.wolfram.com/TopologicalClosure.html