$\forall$$T$:Type, ${\it as}$:$T$ List, $f$, $g$:($T$$\rightarrow\mathbb{B}$).
\\[0ex]priority{-}select($f$;$g$;${\it as}$) $=$ inr($\cdot$) $\in$ $\mathbb{B}$+Unit $\Leftrightarrow$ ($\forall$$a$$\in$${\it as}$. $\neg$$f$($a$) \& $\neg$$g$($a$))