@article{estruch2006distance,
  title={Distance-Based Generalisation Operators for Graphs},
  author={Estruch, V. and Ferri, C. and Hern{\'a}ndez-Orallo, J. and Jos{\'e}, M.},
  journal={Gärtner, Thomas; Garriga, Gemma C.; Meinl, Thorsten (eds.) Proc. of the International WS on Mining and Learning with Graphs, MLG},
  pages={133},
  year={2006}
}