Suppose $ foldn : A \times (A \rightarrow A) \rightarrow \mathbb{N} \rightarrow A $ such that $foldn$ is structural recursion over naturals.
$foldn(c,h,m) = \left\{ \begin{array}{ll} c & \quad m = 0 \\ foldn (h (c), h) \: n & \quad m = succ\: n \end{array} \right. $
In 'The Algebra of Programming' by Richard Bird 1.6 he asks me to find some $f$ such that $foldn(succ,f)$ is equivalent to $curry \: ack$. Could I have a hint please?
Also what is the significance that non primitive recursions can be written in terms of $foldn$?