\begin{tabbing}
$\forall$$X$, $Y$:${\it ik}$:LocKnd fp$\rightarrow$ Top, ${\it ik}$:LocKnd.
\\[0ex]interface{-}union($X$;$Y$)(${\it ik}$)
\\[0ex]$\sim$
\\[0ex]($\lambda$$s$,$v$. if ${\it ik}$ $\in$ dom($X$)
\\[0ex]then \=if ${\it ik}$ $\in$ dom($Y$)\+
\\[0ex]then \=case $X$(${\it ik}$)($s$,$v$)\+
\\[0ex]o\=f inl($x$) =$>$ inl inl $x$  \+
\\[0ex]$\mid$ inr($x$) =$>$ case $Y$(${\it ik}$)($s$,$v$) of inl($x$) =$>$ inl (inr $x$ )  $\mid$ inr($x$) =$>$ inr $x$ 
\-\-\\[0ex]else case $X$(${\it ik}$)($s$,$v$) of inl($x$) =$>$ inl inl $x$   $\mid$ inr($x$) =$>$ inr $x$ 
\\[0ex]fi 
\-\\[0ex]else case $Y$(${\it ik}$)($s$,$v$) of inl($x$) =$>$ inl (inr $x$ )  $\mid$ inr($x$) =$>$ inr $x$ 
\\[0ex]fi )
\end{tabbing}