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;

theorem Th54:
  MemberFunc ({}A, A).x = 0
proof
  UAp {}A = {} by Th19;
  then (UAp {}A)` = [#] A;
  hence thesis by Th41;
end;
