\begin{tabbing}
nullset($p$;$S$)
\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$\=$\forall$$q$:\{$q$:$\mathbb{Q}\mid$ 0 $<$ $q$\} .\+
\\[0ex]$\exists$\=$C$:p{-}open($p$)\+
\\[0ex](($\forall$$s$:($\mathbb{N}\rightarrow$p{-}outcome($p$)). ($S$($s$)) $\Rightarrow$ p{-}open{-}member($p$;$C$;$s$)) \& p{-}measure{-}le($p$;$C$;$q$))
\-\-
\end{tabbing}