\begin{tabbing}
$\forall$$A$:Type, ${\it eq}$:EqDecider($A$), $B$:($A$$\rightarrow$Type), $f$,$g$,$h$:fpf($A$; $a$.$B$($a$)).
\\[0ex]fpf{-}compatible($A$; $a$.$B$($a$); ${\it eq}$; $f$; $g$)
\\[0ex]$\Rightarrow$ \=(fpf{-}compatible($A$; $a$.$B$($a$); ${\it eq}$; $h$; fpf{-}join(${\it eq}$; $f$; $g$))\+
\\[0ex]$\Leftarrow\!\Rightarrow$ (fpf{-}compatible($A$; $a$.$B$($a$); ${\it eq}$; $h$; $f$) $\wedge$ fpf{-}compatible($A$; $a$.$B$($a$); ${\it eq}$; $h$; $g$)))
\-
\end{tabbing}