Λ-set

Definition

• Let (X,τ) be a topological space. A subset S of X is called a Λ-set if it is equal to the intersection of all open supersets of S.

Reference

• Caldas Miguel, Jafari Saeid, Navalagi Govindappa, More on λ-closed sets in topological spaces.,Rev. Colombiana Mat. 41 (2007), no. 2, 355-369.