\begin{definition}[Definition:Permutation/Ordered Selection/Notation]
The number of $r$-permutations from a set of cardinality $n$ is denoted variously:
:$P_{n r}$
:${}^r P_n$
:${}_r P_n$
:${}_n P_r$ (extra confusingly)
There is little consistency in the literature).
On {{ProofWiki}} the notation of choice is ${}^r P_n$.
Category:Definitions/Permutation Theory
\end{definition}