*Definition [#sf765b0f]
-A topological space (X,τ) is said to be λ-D_1 if for any x, y ∈ X such that &ref(http://www.eaflux.com/imgtex/imgtex.fcgi?%5bres=100%5d%7b%5c%5b%20x%5cneq%20y%20%5c%5d%7d%25.png); there exists an [[λ-D-set>λ-Difference set]] of X containing x but not y and a λ-D-set containing y but not x .

*Property [#ke5c0cb9]
-λ_D_1 ⇔ [[λ-D_2]].
-λ_D_1 ⇒ [[λ-D_0]].

*Reference [#c3b5568a]
-Caldas Miguel, Jafari Saeid, Navalagi Govindappa, ''More on λ-closed sets in topological spaces.'',Rev. Colombiana Mat. 41 (2007), no. 2, 355-369.