Definition:Permutation/Ordered Selection/Notation

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Definition

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 $\mathsf{Pr} \infty \mathsf{fWiki}$ the notation of choice is ${}^r P_n$.