\begin{definition}[Definition:Concatenation of URM Programs]
Let $P$ and $Q$ be URM programs.
The '''concatenation of $P$ and $Q$''' is denoted $P * Q$.
It consists of program $P$ followed immediately by program $Q$.
If $P$ and $Q$ compute particular functions, then it is usually necessary to make modifications to either $P$ or $Q$, or both, to make sure that the concatenated program continues to compute a function.
The simplest concatenation is illustrated in Composition of One-Variable URM Computable Functions.
\end{definition}