Last-modified: 2010-09-01 (水) 22:19:22
Let X be a topological space and let A be its subset. A point x is called a θ-cluster point of A if 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.
Mohammad Saleh, Onθ-closed sets and some forms of continuity, Archivum mathematicum (BRNO) Tomus 40 (2004), 383-393.