Boundary (topology) - Wikipedia
https://en.wikipedia.org/wiki/Boundary_(topology)There are several equivalent definitions for the boundary of a subset of a topological space which will be denoted by or simply if is understood: 1. It is the closure of minus the interior of in : ∂ S := S ¯ ∖ int X S {\displaystyle \partial S~:=~{\overline {S}}\setminus \operatorname {int} _{X}S} where denotes the closure of in and denotes the topological interior of in
Boundary Point of a Set | eMathZone
www.emathzone.com › boundary-point-of-a-setBoundary Point of a Set Let A be a subset of a topological space X, a point x ∈ X is said to be boundary point or frontier point of A if each open set containing at x intersects both A and A c. The set of all boundary points of a set A is called the boundary of A or the frontier of A. It is denoted by F r ( A).
Boundary Point -- from Wolfram MathWorld
mathworld.wolfram.com › BoundaryPointDec 17, 2021 · Boundary Point -- from Wolfram MathWorld Topology > Point-Set Topology > Boundary Point A point which is a member of the set closure of a given set and the set closure of its complement set. If is a subset of , then a point is a boundary point of if every neighborhood of contains at least one point in and at least one point not in .