$\forall$$A$:Type, $B$:($A$$\rightarrow$Type), ${\it eq}$:EqDecider($A$), $f$, $g$:$a$:$A$ fp$\rightarrow$ $B$($a$), $x$:$A$.
\\[0ex]$x$ $\in$ dom($f$ $\oplus$ $g$) $\Rightarrow$ $f$ $\oplus$ $g$($x$) $=$ if $x$ $\in$ dom($f$)$\rightarrow$ $f$($x$) else $g$($x$) fi $\in$ $B$($x$)