$\forall$$A$:Type, $f$:($A$$\rightarrow\mathbb{Z}$), $L$:($A$ List). (0 $<$ $\parallel$$L$$\parallel$) $\Rightarrow$ ($\exists$$a$$\in$$L$.$\forall$$x$$\in$$L$. ($f$($x$)) $\leq$ ($f$($a$)))