theorem Th6:
  d is_a_left_unity_wrt F implies EqClass(RD,d) is_a_left_unity_wrt F/\/RD
proof
  defpred P[Element of Class RD] means (F/\/RD).(EqClass(RD,d),$1) = $1;
  assume
A1: F.(d,a) = a;
A2: now
    let a;
    (F/\/RD).(EqClass(RD,d),EqClass(RD,a)) = Class(RD, F.(d,a)) by Th3
      .= EqClass(RD, a) by A1;
    hence P[EqClass(RD,a)];
  end;
  thus for c being Element of Class RD holds P[c] from SchAux1(A2);
end;
