\begin{tabbing}
$a$ $\div\downarrow$ $n$
\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$\=if\= 0 $\leq$z $a$\+\+
\\[0ex]then $a$ $\div$ $n$
\-\\[0ex]if (({-}$a$) rem $n$ =$_{0}$ 0) then {-}(({-}$a$) $\div$ $n$) else ({-}(({-}$a$) $\div$ $n$))+({-}1) fi 
\-
\end{tabbing}