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