4. [It] marks] In your lectures, we have discussed that for certain types of smoothers, given the smoothing matrix 3),, there exist a computational for- mula for computing the cross validation criterion which does not require the deletion of each point and ret, hence greatly reducing the computational burden. Such smoothers havethe property that, if we add a new point {ar.,-,y,;} to the existing tted curve f". based on n 1 points, and if 3;,- lies on the curve 3"\