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