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

\bibitem{handbook}
H~Ehrig, G~Engels, H-J Kreowski, and G~Rozenberg.
\newblock {\em Handbook of Graph Grammand and Computing by Graph
  Transformation}.
\newblock World Scientific, 1997.

\bibitem{RET}
R.~E. Tarjan.
\newblock {\em Data Structures and Network Algorithms}.
\newblock SIAM, 1983.

\end{thebibliography}