10. A subset A of a topological space (X,T) is said to be semi-open if there exists an open set 0 = (X,T) such that OCACO. Verify the following: (i) every open set is a semi-open set; (ii) a closed set is not necessarily a semi-open set; (iii) if A is an interval other than a singleton set in R, then A is a semi-open subset of R; (iv) if T is the finite-closed topology, the discrete topology or the indiscrete topology then the semi-open sets are precisely the open sets.