*Deinition [#qe96a4f5]
-A subset A of a topological space (X,τ) is said to be δ-semiopen set if there exists a [[δ-open]] set U of X such U ⊂ X ⊂ Cl(U).

*Reference [#ob1574bd]
-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.