$\forall$$T$:Type, ${\it as}$:($T$ List), $f$,$g$:($T$$\rightarrow\mathbb{B}$).
\\[0ex](priority{-}select($f$; $g$; ${\it as}$) = (inr $\cdot$ ) $\in$ (?$\mathbb{B}$))
\\[0ex]$\Leftarrow\!\Rightarrow$ l\_all(${\it as}$; $T$; $a$.(($\neg$($\uparrow$($f$($a$)))) $\wedge$ ($\neg$($\uparrow$($g$($a$))))))