nullset($p$;$S$)
\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$$\forall$$q$:\{$q$:$\mathbb{Q}\mid$ 0 $<$ $q$\} . $\exists$$C$:p{-}open($p$). (($\forall$$s$:($\mathbb{N}\rightarrow$Outcome). ($S$($s$)) $\Rightarrow$ $s$ $\in$ $C$) \& measure($C$) $\leq$ $q$)