θ-open

Last-modified: 2010-09-01 (水) 22:19:22

Definition

Let X be a topological space and let A be its subset. A point x is called a θ-cluster point of A if imgtex.fcgi?%5bres=100%5d%7b$A%5ccap%5cmathrm%7bcl%7dU%5cneq%20%5cemptyset$%7d%25.png for every open neighborhood of x. A is called θ-closed if it contains all θ-cluster points of itself. A is called θ-open if the complement of A is θ-closed.

Reference

Mohammad Saleh, Onθ-closed sets and some forms of continuity, Archivum mathematicum (BRNO) Tomus 40 (2004), 383-393.