δ-interior

Definition

• The δ-interior of a subset A of a topological space (X,τ), denoted by , is the union of all regular open sets of (X,τ) contained in A.

Reference

• Caldas, M.; Ganster, M.; Georgiou, D. N.; Jafari, S.; Moshokoa, S. P., δ-semiopen sets in topology. (English summary), Proceedings of the 19th Summer Conference on Topology and its Applications., Topology Proc. 29 (2005), no. 2, 369–383.