In how many ways may we label the elements of a k element set with n distinct labels (numbered 1 through n) so that label i is used ji times? ( If we think of the labels as y1, y2, . . . , yn, then we can rephrase this question as follows. How many functions are there from a k-element set K to a set N = {y1, y2, . . . yn} so that each yi is the image of ji elements of K?)