reserve T for TopSpace;
reserve T for non empty TopSpace;
reserve F for Subset-Family of T;
reserve T for non empty TopSpace;

theorem Th63:
  for A, B being Subset of T st B is open_condensed holds A c= B
  implies Int(Cl(A \/ B)) = B
proof
  let A, B be Subset of T;
  assume
A1: B is open_condensed;
  assume A c= B;
  then A \/ B = B by XBOOLE_1:12;
  hence thesis by A1,TOPS_1:def 8;
end;
