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. | 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. |