let T be non empty TopSpace; :: thesis: for F being Subset-Family of T holds union (Int (Cl (Int F))) c= Int (Cl (Int (union F)))
let F be Subset-Family of T; :: thesis: union (Int (Cl (Int F))) c= Int (Cl (Int (union F)))
A1: Int (union (Cl (Int F))) c= Int (Cl (Int (union F))) by Th48, TOPS_1:19;
union (Int (Cl (Int F))) c= Int (union (Cl (Int F))) by Th27;
hence union (Int (Cl (Int F))) c= Int (Cl (Int (union F))) by A1; :: thesis: verum