\begin{tabbing}
(\=(((((((((Unfold `fseg` 0) \+
\\[0ex]CollapseTHEN ((Auto\_aux (first\_nat 1:n) ((first\_nat 1:n
\-\\[0ex])\=,(first\_nat 3:n)) (first\_tok :t) inil\_term)))$\cdot$) \+
\\[0ex]CollapseTHEN (ExRepD))$\cdot$) 
\\[0ex]
\\[0ex]CollapseTHEN (HypSubst ({-}1) 0))$\cdot$) 
\\[0ex]CollapseTHEN ((Auto\_aux (first\_nat 1:n) ((first\_nat 
\-\\[0ex]1\=:n),(first\_nat 3:n)) (first\_tok :t) inil\_term)))$\cdot$) \+
\\[0ex]CollapseTHEN (((
\-\\[0ex]R\=WO "length\_append" 0) \+
\\[0ex]CollapseTHEN ((Auto\_aux (first\_nat 1:n) ((first\_nat 2:n
\-\\[0ex]),(first\_nat 3:n)) (first\_tok SupInf:t) inil\_term)))$\cdot$))$\cdot$
\end{tabbing}