reserve a,b,c,d for Real;
reserve z,z1,z2 for Complex;

theorem Th20:
  Re(z") = Re z / ((Re z)^2+(Im z)^2) &
  Im(z") = (- Im z) / ((Re z)^2+(Im z)^2)
proof
  z" = Re z / ((Re z)^2+(Im z)^2)+((- Im z) / ((Re z)^2+(Im z)^2))*<i>
  by Lm24;
  hence thesis by Th12;
end;
