*Definition [#r9fc24f3]
-A topological space (X,τ) is said to be C_0 if for every x∈X, {x}' is not union of non-empty closed sets.

*Property [#r1bc9725]
-C_0 + [[T_0]] = [[T_1]].
-C_0 ⇒ [[R_D]].
-C_0 ⇒ [[T_1∨(∖T_{UD})>T_1∨(|T_{UD})]].

*Reference [#ffb2b876]
-Guia, Josep, ''Essentially T_D and essentially T_UD spaces.'', Bull. Math. Soc. Sci. Math. R. S. Roumanie (N.S.) 32(80) (1988), no. 3, 227-233.