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{\large Addendum to \\[1ex]}
\textbf{\Large A Census of Vertices by Generations \\in Regular Tessellations of the Plane}\\[2ex]
{\large Alice Paul\qquad Nicholas Pippenger\\[2ex]}
Aug.\ 30, 2012
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Three additional references should be added to our paper: 
\begin{itemize}
\item J. W. Cannon, ``The combinatorial structure of cocompact discrete hyperbolic groups'', \emph{Geom.\ Dedicata}, 16 (1984) 
123--148, 
\item J. F. Moran, ``The growth rate and balance of homogeneous tiiings in the hyperbolic plane'', \emph{Discrete Math.}, 173 (1997) 151--186
\item S. Graves, T. Pisanski and M. E. Watkins, ``Growth of edge-homogeneous tessellations'', \emph{SIAM J. Discrete Math.},
23:1 (2008) 1-18.
\end{itemize}  The first of these papers appears to be the first to observe that the generating functions for problems such as we study are rational; the other two, while focusing on the asymptotic growth rate rather than the complete generating function, deal with tessellations considerably more general than those dealt with in our paper.
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