public static PointDbl Subtract(this PointDbl lhs, PointDbl rhs) { return new PointDbl ( y: (lhs.Y - rhs.Y), x: (lhs.X - rhs.X) ); }
public static PointDbl Add(this PointDbl lhs, PointDbl rhs) { return new PointDbl ( x: (lhs.X + rhs.X), y: (lhs.Y + rhs.Y) ); }