*Definition [#r3f68f65]
-A subset S of a topological space (X,τ) is called λ-open if the complement of S is [[λ-closed]].

*Reference [#w3f08257]
-Caldas Miguel, Jafari Saeid, Navalagi Govindappa, ''More on λ-closed sets in topological spaces.'',Rev. Colombiana Mat. 41 (2007), no. 2, 355-369.