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diff --git a/doc/documentation.tex b/doc/documentation.tex
index 956a10e..9efc3ad 100644
--- a/doc/documentation.tex
+++ b/doc/documentation.tex
@@ -345,6 +345,22 @@ works as follows:
 \item The chain of recursive calls unravels until the call to
   \texttt{CCTK\_InterpGridArrays} returns.
 \end{enumerate}
+\begin{figure}[tb]
+\begin{center}
+\includegraphics[scale=.833,clip=true]{fig/recursion.eps}
+\end{center}
+\caption[Symmetry interpolation] {
+  The recursive calls involved in symmety interpolation.
+  Values of grid functions $a$ at global cartesian coordinates $x$ are 
+  calculated by nested calls to the symmetry interpolators, which first
+  apply the symmetry transformation to the coordinates.  When all
+  the symmetries have been applied, the local interpolator is called,
+  producing the interpolation of grid function values in the local basis.
+  As the symmetry interpolators return, they apply the inverse basis
+  transformation to the interpolated grid function values.
+}
+\label{SymBase_recursion}
+\end{figure}
 
 This mechanism has thus four players:
 \begin{itemize}