\begin{tabbing}
scheme{-}plus($A$;$B$)
\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$\=let ${\it na}$,${\it La}$,${\it Ra}$ = $A$ in \+
\\[0ex]let ${\it nb}$,${\it Lb}$,${\it Rb}$ = $B$ in $<$${\it na}$+${\it nb}$, ${\it La}$ @ ${\it Lb}$, $\lambda$${\it nmr}$.(${\it Ra}$(${\it nmr}$)) $\oplus$ (${\it Rb}$(namer{-}shift(${\it na}$;${\it nmr}$)))$>$
\-
\end{tabbing}