semi-open

Definition

• Let (X, τ) be a topological space. A subset S ⊆ X is called semi-open if there exists a open set O such that O ⊆ S ⊆ Cl(O).

Property

• Every semi-open set is sg-open but the converse is not true.

Reference

• Bhattacharyya Paritosh, Lahiri B. K., Semigeneralized closed sets in topology., Indian J. Math. 29 (1987), no. 3, 375-382 (1988).