*Definition [#a0d8d022]
-A subset S ⊂ X is called a λ-Difference set (in short λ-D-set), if there
are two λ-open sets U , V in X such that &ref(http://www.eaflux.com/imgtex/imgtex.fcgi?%5bres=100%5d%7b%5c%5b%20U%5cneq%20X%5cmbox%7b%20and%20%7dS=%20U%5csetminus%20V%20%5c%5d%7d%25.png);.

*Reference [#e74ce655]
-Caldas Miguel, Jafari Saeid, Navalagi Govindappa, ''More on λ-closed sets in topological spaces.'',Rev. Colombiana Mat. 41 (2007), no. 2, 355-369.