@inproceedings{UpdateSemanticsNlis98,
  author = {Torre, L.W.N. van der, and Tan, Y.-H.},
  title = {An Update Semantics for Deontic Reasoning},
  booktitle = {International Workshop on Natural Language and Information Systems NLIS'98},
  year = {1998},
  url = {http://icr.uni.lu/leonvandertorre/papers/nlis98.ps.Z}
}