\begin{tabbing}
(\=(((((Unfold `last` 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 (Reduce 0))$\cdot$) 
\\[0ex]
\\[0ex]C\=ollapseTHEN (Assert $\parallel$$L$$\parallel$ $>$ 0  \+
\\[0ex]THENL [((((RW assert\_pushdownC ({-}1)) 
\-\\[0ex]CollapseTHENA (
\-\\[0ex](\=Auto\_aux (first\_nat 1:n) ((first\_nat 1:n),(first\_nat 3:n)) (first\_tok :t) inil\_term)))$\cdot$)\+
\\[0ex]
\\[0ex]Collaps\=eTHEN (Easy))$\cdot$; \+
\\[0ex]((RWO "select\_cons\_tl" 0) 
\-\\[0ex]CollapseTHEN (
\-\\[0ex](Auto\_aux (first\_nat 1:n) ((first\_nat 2:n),(first\_nat 3:n)) (first\_tok :t) inil\_term)))$\cdot$]
\\[0ex]))$\cdot$
\end{tabbing}