@InProceedings{penn:2001:ACL,
  author    = {Gerald Penn},
  title     = {Tractability and Structural Closures in Attribute Logic Type Signatures},
  booktitle = {Proceedings of 39th Annual Meeting of the Association for Computational Linguistics},
  month     = {July},
  year      = {2001},
  address   = {Toulouse, France},
  publisher = {Association for Computational Linguistics},
  pages     = {418--425},
  url       = {http://www.aclweb.org/anthology/P01-1054},
  doi       = {10.3115/1073012.1073066}
}