*Definition [#pba0d918]
-Let S be a subset of a topological space (X, τ). The set of all [[λ-cluster points>λ-cluster point]] of S is called the λ-closure of S and is denoted by &ref(http://www.eaflux.com/imgtex/imgtex.fcgi?%5bres=100%5d%7b%5c%5b%20%5crm%7bCl%7d_%5clambda%28S%29%20%5c%5d%7d%25.png);.

*Reference [#z33fa677]
-Caldas Miguel, Jafari Saeid, ''On some low separation axioms via λ-open and λ-closure operator.'',  Rend. Circ. Mat. Palermo (2) 54 (2005), no. 2, 195–208.