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

theorem Th53:
  |.z*'.| = |.z.|
proof
  thus |.z*'.| = sqrt ((Re z)^2 + (Im (z*'))^2) by Th27
    .= sqrt ((Re z)^2 + (-Im z)^2) by Th27
    .= |.z.|;
end;
