\begin{tabbing}
chain{-}config(${\it es}$;${\it Sys}$;${\it chain}$)
\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$\=($\forall$$e$:E(${\it Sys}$). no\_repeats(Id;${\it chain}$($e$)) \& (0 $<$ $\parallel$${\it chain}$($e$)$\parallel$) \& (loc($e$) $\in$ ${\it chain}$($e$)))\+
\\[0ex]\& ($\forall$$e$, ${\it e'}$:E(${\it Sys}$). ${\it chain}$($e$) $\subseteq$ ${\it chain}$(${\it e'}$) $\vee$ ${\it chain}$(${\it e'}$) $\subseteq$ ${\it chain}$($e$))
\\[0ex]\& ($\forall$$e$, ${\it e'}$:E(${\it Sys}$). ($e$ $<$loc ${\it e'}$) $\Rightarrow$ ${\it chain}$(${\it e'}$) $\subseteq$ ${\it chain}$($e$))
\-
\end{tabbing}