$\forall$$A$:Type, ${\it eq}$:EqDecider($A$), $f$, $g$:$a$:$A$ fp$\rightarrow$ Top, $L$:($A$ List).
\\[0ex]l\_disjoint($A$;$f$ $\oplus$ $g$.1;$L$) $\Leftarrow\!\Rightarrow$ (l\_disjoint($A$;$f$.1;$L$) \& l\_disjoint($A$;$g$.1;$L$))