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$\forall$$E$,$X_{1}$,$X_{2}$:Type, ${\it info}$:($E$$\rightarrow$((:Id $\times$ $X_{1}$) + (:(:IdLnk $\times$ $E$) $\times$ $X_{2}$))), ${\it pred?}$:($E$$\rightarrow$(?$E$)).
\\[0ex]SWellFounded(pred!($e$;${\it e'}$))
\\[0ex]$\Rightarrow$ ($\forall$$e$:$E$. ($\neg$($\uparrow$first($e$))) $\Rightarrow$ (loc(pred($e$)) = loc($e$) $\in$ Id))
\\[0ex]$\Rightarrow$ ($\forall$$e$,${\it e'}$:$E$. (loc($e$) = loc(${\it e'}$) $\in$ Id) $\Rightarrow$ (${\it pred?}$($e$) = ${\it pred?}$(${\it e'}$)) $\Rightarrow$ ($e$ = ${\it e'}$))
\\[0ex]$\Rightarrow$ \=($\forall$$e$,${\it e'}$:$E$.\+
\\[0ex](loc($e$) = loc(${\it e'}$) $\in$ Id)
\\[0ex]$\Rightarrow$ $e$ $<$ ${\it e'}$
\\[0ex]$\Rightarrow$ ($e$ rel\_plus($E$; ($\lambda$$x$,$y$. ($\neg$($\uparrow$first($y$))) c$\wedge$ ($x$ = pred($y$) $\in$ $E$))) ${\it e'}$))
\-
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