User:IssaRice/Computability and logic/Index and program

In computability theory, if we have some numbering $\varphi _{0},\varphi _{1},\varphi _{2},\ldots$ of computable partial functions then the number $e$ is called the index of $\varphi _{e}$, i.e., $\varphi _{e}$ is the $e$th computable partial function.

We can also think of $e$ as the source code of an algorithm computing $\varphi _{e}$.