[18] M. Pelillo, K. Siddiqi, and S.W. Zucker. Matching hierarchical structures using association graphs. *IEEE Transactions on Pattern Analysis and Machine Intelligence*,
21(11):1105–1120, 1999.

[19] J.W. Raymond, E.J. Gardiner, and P. Willett. RASCAL: Calculation of graph similarity using maximum common edge subgraphs. *Computer Journal*, 45(6):631–
644, 2002.

[20] K. Schädler and F. Wysotzki. Comparing structures using a Hopfield-style neural network. *Applied Intelligence*, 11:15–30, 1999.

[21] R.C. Wilson and E.R. Hancock. Structural matching by discrete relaxation. *IEEE*
Transactions on Pattern Analysis and Machine Intelligence, 19(6):634–648, 1997.