\begin{tabbing}
(\% This side doesn't need decidability \% 
\\[0ex](\=(((InstHyp [$x$;$y$] 4) \+
\\[0ex]CollapseTHENM (ProveProp
\-\\[0ex])\=)$\cdot$) \+
\\[0ex]CollapseTHENA ((Auto\_aux (first\_nat 1:n) ((first\_nat 1:n),(first\_nat 3:n
\-\\[0ex])) (first\_tok :t) inil\_term)))$\cdot$)
\end{tabbing}