@InProceedings{Lutz-Wolter-CADE-07,
  author = 	 {Carsten Lutz and Frank Wolter},
  title = 	 {Conservative Extensions in the Lightweight Description Logic $\mathcal{EL}$},
  booktitle = 	 {Proceedings of the 21th Conference on Automated Deduction (CADE-21)},
  year = 	 {2007},
  pages =        {84--99},
  editor =       {Frank Pfenning},
  publisher =    {Springer-Verlag},
  series =	 {Lecture Notes in Artificial Intelligence},
  volume =       {4603},
  springer =     {yes}
}