reserve T for TopSpace;

theorem Th27:
  for F being Subset-Family of T holds union(Int F) c= Int(union F )
proof
  let F be Subset-Family of T;
A1: Int union(Int F) c= Int(union F) by Th25,TOPS_1:19;
  union(Int F) is open by Th17,TOPS_2:19;
  hence thesis by A1,TOPS_1:23;
end;
