$\forall$$A$:Type, ${\it eq}$:EqDecider($A$), $B$:($A$$\rightarrow$Type), $f$, $g$, $h$:$a$:$A$ fp$\rightarrow$ $B$($a$).
\\[0ex]$f$ $\parallel$ $h$ $\Rightarrow$ $g$ $\parallel$ $h$ $\Rightarrow$ $f$ $\oplus$ $g$ $\parallel$ $h$