\begin{tabbing}
(\=(Using [`L2',[$x$; $y$; $z$]] (BackThruLemma `sublist\_transitivity`)) \+
\\[0ex]CollapseTHEN (
\-\\[0ex](Auto\_aux (first\_nat 1:n) ((first\_nat 1:n),(first\_nat 3:n)) (first\_tok :t) inil\_term)))$\cdot$
\end{tabbing}