\begin{tabbing}
let $a$,$b$,$c$,$d$,$e$,$f$ = $u$ in $v$($a$;$b$;$c$;$d$;$e$;$f$)
\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$\=let $a$,${\it zz}_{1}$ = $u$\+
\\[0ex]in
\\[0ex]let $b$,${\it zz}_{2}$ = ${\it zz}_{1}$
\\[0ex]in
\\[0ex]let $c$,${\it zz}_{3}$ = ${\it zz}_{2}$ in let $d$,${\it zz}_{4}$ = ${\it zz}_{3}$ in let $e$,$f$ = ${\it zz}_{4}$ in $v$($a$;$b$;$c$;$d$;$e$;$f$)
\-
\end{tabbing}