In a topological space , an open neighborhood of a point is an open set containing . A set containing an open neighborhood is simply called a neighborhood.
Open Neighborhood
See also
Neighborhood, Open SetThis entry contributed by Margherita Barile
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Barile, Margherita. "Open Neighborhood." From MathWorld--A Wolfram Web Resource, created by Eric W. Weisstein. https://mathworld.wolfram.com/OpenNeighborhood.html