reserve T for 1-sorted;
reserve T for TopSpace;

theorem Th5:
  for A being Subset of T holds Int Cl A = Int Cl Int Cl A
proof
  let A be Subset of T;
A1: Int Int Cl A c= Int Cl Int Cl A by PRE_TOPC:18,TOPS_1:19;
  Int Cl Int Cl A c= Int Cl A by Th3,TOPS_1:19;
  hence thesis by A1;
end;
