Axiom:Axioms of Uncertainty/Axiom 2

Axiom
$H_n$ fulfils the following axiom: For any permutation $\pi$ of $\tuple {1, 2, \dotsc, n}$:
 * $\map {H_n} {p_1, p_2, \ldots, p_n} = \map {H_n} {p_{\map \pi 1}, p_{\map \pi 2}, \ldots, p_{\map \pi n} }$

That is, $H_n$ is a symmetric function of the arguments $p_1, p_2, \dotsc, p_n$.