semi-kernel of x

Definition

• Let (X,τ) be a topological space and x∈X. The semi-kernel of x denoted by s-ker(x) is equal to
  ∩{U| U is a semi-open set and x∈U}.

Reference

• Arya, S.P.; Nour, T.M., Weakly semi-R_0 spaces., (English) [J] Indian J. Pure Appl. Math. 21, No.12, 1083-1085 (1990).