*Definition [#w74a6474]
-For a subset A of X, the intersection of all [[β-closed]] sets of X containing A is called the β-closure (in short β-cl(A)) of A.

*Reference [#dd378ec7]
-Basu, C. K.; Afsan, B. M. Uzzal; Ghosh, M. K., ''A class of functions and separation axioms with respect to an operation.'' (English summary), Hacet. J. Math. Stat. 38 (2009), no. 2, 103-118.