\begin{thebibliography}{1}

\bibitem{Reduction}
Stefan Arnborg, Bruno Courcelle, Andrzej Proskurowski, and Detlef Seese.
\newblock An algebraic theory of graph reduction.
\newblock {\em Journal of the ACM (JACM)}, 40(5):1134--1164, 1993.

\bibitem{p3t}
Stefan Arnborg and Andrzej Proskurowski.
\newblock Characterization and recognition of partial 3-trees.
\newblock {\em SIAM J. Alg. Disc. Meth.}, 7:305--314, 1986.

\bibitem{parameterized}
R.~G. Downey and M.~R. Fellows.
\newblock {\em Parameterized Complexity}.
\newblock Springer, 1999.

\end{thebibliography}