*Definition [#e6d0c121]
-A topological space (X,τ) is said to be semi-R_1 if for each pair x,y in X such that &ref(http://www.eaflux.com/imgtex/imgtex.fcgi?%5bres=100%5d%7b%5c%5b%20%5cmbox%7bs-cl%7d%28%5c%7bx%5c%7d%29%5cneq%5cmbox%7bs-cl%7d%28%5c%7by%5c%7d%20%5c%5d%7d%25.png);, there exist disjoint [[semi open]]sets U and V such that &ref(http://www.eaflux.com/imgtex/imgtex.fcgi?%5bres=100%5d%7b%5c%5b%20%5cmbox%7bs-cl%7d%28%5c%7bx%5c%7d%29%5csubset%20U%20%5cmbox%7b%20and%20%7d%5cmbox%7bs-cl%7d%28%5c%7by%5c%7d%5csubset%20V%20%5c%5d%7d%25.png);.

*Reference [#df486233]
-Dorsett, C., ''Images and hyperspaces of s-essentially T_1 and s-essentially T_2 spaces and semitopological properties.'' (Serbo-Croatian summary), Glas. Mat. Ser. III 21(41) (1986), no. 2, 415–422.