*Definition [#u5fe2064]
-A topological space (X,τ) is said to be pre-R_0 if every [[pre-open]] set contains the [[pre-closure]] of each of its singletons.

*Reference [#v4352f49]
-Caldas, M.; Georgiou, D. N.; Jafari, S. , ''Characterizations of low separation axioms via α-open sets and α-closure operator.'', (English summary) Bol. Soc. Parana. Mat. (3) 21 (2003), no. 1-2, 97–111.