6.3 () The nearest-neighbour classifier (Section 2.5.2) assigns a new input vector x to the same class as that of the nearest input vector xn from the training set, where in the simplest case, the distance is defined by the Euclidean metric x − xn2. By expressing this rule in terms of scalar products and then making use of kernel substitution, formulate the nearest-neighbour classifier for a general nonlinear kernel.