 In this case, the “unknown” function denoted by \(\phi(x)\) is specified in terms of the auxiliary function \(\psi(x)\) in such a way that \(\phi(x)\) appears only once on the lefthand side of the equations (other than the base case). Nonetheless, such a system of equations is unlike a primitive recursive definition in that it does not specify a unique means for computing the values of \(\phi(n)\) by “deconstructing” \(n\) in the deterministic manner illustrated by calculations such as (\ref{factcalc}).