\begin{tabbing}
$\forall$$p$,$q$:$\mathbb{Z}$.
\\[0ex]spreadn(\=gcd\_reduce($p$; $q$);\+
\\[0ex]$g$,$a$,$b$.(($p$ = ($a$ $\ast$ $g$)) $\wedge$ ($q$ = ($b$ $\ast$ $g$)) $\wedge$ coprime($a$; $b$) $\wedge$ (($p$ $\ast$ $b$) = ($a$ $\ast$ $q$))))
\-
\end{tabbing}