\begin{definition}[Definition:Primitive Recursion/One Variable]
Let $a \in \N$ be a natural number.
Let $g: \N^2 \to \N$ be a function.
Then the function $h: \N \to \N$ is '''obtained from the constant $a$ and $g$ by primitive recursion''' {{iff}}:
:$\forall n \in \N: \map h n = \begin {cases}
a & : n = 0 \\
\map g {n - 1, \map h {n - 1} } & : n > 0 
\end{cases}$
\end{definition}