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