$\forall$$p$:FinProbSpace, $n$, $m$:$\mathbb{N}$. ($n$ $\leq$ $m$) $\Rightarrow$ ($\forall$$X$:RandomVariable($p$;$n$). E($n$;$X$) = E($m$;$X$) $\in$ $\mathbb{Q}$)