\begin{tabbing}
$a\:$\=$:= 0$; \kill
$a$\>$:= 0$; \\
$b$\>$:= 1$; \\
$i$\>$:= 0$; \\
$\mathbf{while}\ n \ne i\ \mathbf{do}$ \\
\pushtabs
\hspace*{1em}\=$($\=$b\:$\=$:= a + b$; \kill
\>$($\>$b$\>$:= a + b$; \\
\>\>$a$\>$:= b - a$; \\
\>\>$i$\>$:= i + 1)$; \\
\poptabs
$p$\>$:= a$
\end{tabbing}


