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