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$\forall$\=${\it es}$:ES, ${\it Config}$:AbsInterface(chain\_config()), ${\it Cmd}$:Type, ${\it Sys}$:AbsInterface(chain\_sys(${\it Cmd}$)),\+
\\[0ex]$e$:E(${\it Sys}$).
\-\\[0ex]valid{-}sys(${\it es}$;${\it Config}$;${\it Sys}$;$e$) $\in$ $\mathbb{P}$
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