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Neighbourhood  |  Neighborhood   (English)

Definition (undergraduate level)

In a metric space, the ε neighbourhood of a point P is the set of all points whose distance from P is less than ε.
In a topological space X, a neighbourhood of a point p is any subset of X which contains an open set which contains p.

Definition (undergraduate level)

The subset W of topological space X is a neighbourhood of x ∈ X if there is an open subset U of W with x ∈ U .

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