\begin{tabbing}
(\=(((D 6) \+
\\[0ex]CollapseTHEN (ProveProp))$\cdot$) 
\\[0ex]CollapseTHEN ((Auto\_aux (first\_nat 1:n
\-\\[0ex]) ((first\_nat 1:n),(first\_nat 1000:n)) (first\_tok :t) inil\_term)))$\cdot$
\end{tabbing}