$\forall$$A$:Type, ${\it eq}$:EqDecider($A$), $f$,$g$:fpf($A$; $a$.top), $x$:$A$, $z$:top.
\\[0ex]sqequal(fpf{-}cap(fpf{-}join(${\it eq}$; $f$; $g$); ${\it eq}$; $x$; $z$); fpf{-}cap($f$; ${\it eq}$; $x$; fpf{-}cap($g$; ${\it eq}$; $x$; $z$)))