@inproceedings{krotov-etal-1998-compacting,
    title = "Compacting the {P}enn {T}reebank Grammar",
    author = "Krotov, Alexander  and
      Hepple, Mark  and
      Gaizauskas, Robert  and
      Wilks, Yorick",
    booktitle = "{COLING} 1998 Volume 1: The 17th International Conference on Computational Linguistics",
    year = "1998",
    url = "https://preview.aclanthology.org/ingest-emnlp/C98-1111/"
}