An '''open set''' in [[Euclidean space]] is a set that contains a ball around each of its points. In Euclidean space, a "ball" of radius ''r'' centered at a point ''p'' is the set of all points which are distance at most ''r'' from ''p''. Intuitively, if a point is contained in an open set, then all points sufficiently close to it are also contained.
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An '''open set''' in [[Euclidean space]] is a set that contains a ball around each of its points. Intuitively, if a point is contained in an open set, then all points sufficiently close to it are also contained.
Open sets are the basic objects in [[topology]], in terms of which all other objects are defined.
Open sets are the basic objects in [[topology]], in terms of which all other objects are defined.