*Definition [#ab574d66]
-A topological space (X,τ) is said to be C_D if for every x∈X, either {x}' is empty or {x}' is not closed.

*Property [#t17878a0]
-C_D + [[T_D]] = [[T_1]].

*Reference [#i53ddac1]
-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.