anchor.diff:  
     @override
     Coordinate<T> operator +(math.Point<T> other) =>
  -      Coordinate<T>(x + other.x, y + other.y);
  +      Coordinate<T>(x + other.x as T, y + other.y as T);
   
     Vector toVector() => Vector(x, y);
   
  
positive.code: 
    static Vector<T> difference<T extends num>(
            math.Point<T> a, math.Point<T> b) =>
        Vector<T>(a.x - b.x, a.y - b.y);
  
    static bool valid(math.Point point) =>
        isValidNumber(point.x) && isValidNumber(point.y);
  
negative.code: 
    @override
    Vector<T> operator +(math.Point<T> other) =>
        Vector<T>(x + other.x as T, y + other.y as T);
  
    @override
    Vector<T> operator *(num magnitude) => scale(magnitude);
  