$\forall$${\it as}$:($\mathbb{Q}$ List). $\exists$$a$:$\mathbb{Q}$. ((($\neg$($\uparrow$null(${\it as}$))) $\Rightarrow$ ($a$ $\in$ ${\it as}$)) \& ($\forall$${\it a'}$$\in$${\it as}$. $a$ $\leq$ ${\it a'}$))