@inproceedings{campbell:2004:ACL,
  author    = {Campbell, Richard},
  title     = {Using Linguistic Principles to Recover Empty Categories},
  booktitle = {Proceedings of the 42nd Meeting of the Association for Computational Linguistics (ACL'04), Main Volume},
  year      = 2004,
  month     = {July},
  address   = {Barcelona, Spain},
  pages     = {645--652}
}