reserve A for Tolerance_Space,
  X, Y for Subset of A;
reserve A for Approximation_Space,
  X for Subset of A;
reserve A for finite Tolerance_Space,
  X for Subset of A,
  x for Element of A;
reserve A for finite Approximation_Space,
  X, Y for Subset of A,
  x for Element of A;
reserve A for Tolerance_Space,
  X, Y, Z for Subset of A;

theorem
  X _c=^ Y & Y _c=^ Z implies X _c=^ Z by Th60,Th59;
