\begin{tabbing}
Rtransform($f$;$A$)
\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$\=if Rplus?($A$)\+
\\[0ex]then R{-}plus(Rtransform($f$;Rplus{-}left($A$));Rtransform($f$;Rplus{-}right($A$)))
\\[0ex]else $f$($A$)
\\[0ex]fi 
\-\\[0ex]\emph{(recursive)}
\end{tabbing}