\begin{tabbing}
$\forall$\=${\it es}$:ES, $e_{1}$:E, $e_{2}$:\{$e$:E$\mid$ loc($e$) $=$ loc($e_{1}$) $\in$ Id \}, $p$,\+
\\[0ex]${\it p'}$:(\{$e$:E$\mid$ loc($e$) $=$ loc($e_{1}$) $\in$ Id \}$\rightarrow$\{$e$:E$\mid$ loc($e$) $=$ loc($e_{1}$) $\in$ Id \}$\rightarrow$Prop).
\-\\[0ex](\=$\forall$$a$, $b$:\{$e$:E$\mid$ loc($e$) $=$ loc($e_{1}$) $\in$ Id \}.\+
\\[0ex]($a$ $\in$ [$e_{1}$, $e_{2}$]) $\Rightarrow$ ($b$ $\in$ [$e_{1}$, $e_{2}$]) $\Rightarrow$ \{$p$($a$,$b$) $\Rightarrow$ ${\it p'}$($a$,$b$)\})
\-\\[0ex]$\Rightarrow$ \{[$e_{1}$,$e_{2}$]$\sim$([$a$,$b$].$p$($a$,$b$))+ $\Rightarrow$ [$e_{1}$,$e_{2}$]$\sim$([$a$,$b$].${\it p'}$($a$,$b$))+\}
\end{tabbing}