*Definition [#r4b424ef]
-A topological space X is a R_1 space if any two topologically distinguishable points in X can be [[separated by neighbourhoods]].


*Property [#w2e35054]
-R_1 ⇒ [[mildly Hausdorff]]. [2]
-Every [[S-closed]] R_1 space is [[extremally disconnected]]. 
-Every R_1 topological space is [[presober]]. [3]

*Reference [#p70efd13]
+a
+Dontchev, J.; Popvassilev, S.; Stavrova, D., ''On the η-expansion topology for the co-semi-regularization and mildly Hausdorff spaces.'', (English summary), Acta Math. Hungar. 80 (1998), no. 1-2, 9-19.
+-M.L. Colasante and D. Van der Zypen, ''Minimal R_1, minimal regular and minimal presober topologies'', Revista Notas de Matemática, Vol.5(1),No. 275, 2009, pp.73-84