@inproceedings{UpdateSemanticsNaic97,
  author = {Torre, L.W.N. van der, and Tan, Y.-H.},
  title = {An Update Semantics for Deontic Reasoning},
  year = {1997},
  booktitle = {Proceedings of the 9th Dutch Conference on Artificial Intelligence (NAICÕ97)},
  url = {http://icr.uni.lu/leonvandertorre/papers/naic971.ps.Z}
}