 We have already seen that the addition function \(\textit{add}(x,y)\) can be defined by primitive recursion in terms of repeated application of successor and that the multiplication function \(\mathit{mult}(x,y)\) can be defined by primitive recursion in terms of repeated application of addition.  We can continue this sequence by observing that the exponentiation function \(x^y\) can be defined by primitive recursion in terms of repeated multiplication as follows: 