Definition
- Let be a cover of a set X and x be a point in X. The star of a one-point set {x} with respect to U (, that is, ) is called the star of the point x with respect to U and is denoted by .
Reference
- Engelking, Ryszard, General topology., Translated from the Polish by the author. Second edition. Sigma Series in Pure Mathematics, 6. Heldermann Verlag, Berlin, 1989. viii+529 pp. ISBN: 3-88538-006-4.