public double angle_approx(PlaVectorInt p_other){
  double result=Math.acos(cos_angle(p_other));
  if (side_of(p_other) == PlaSide.ON_THE_LEFT) {
    result=-result;
  }
  return result;
}

public double angle_approx ( PlaVectorInt p_other ) { double result = Math . acos ( cos_angle ( p_other ) ) ; if ( side_of ( p_other ) == PlaSide . ON_THE_LEFT ) { result = - result ; } return result ; }
returns an approximation of the signed angle between this vector and p_other .
