@inproceedings{penn-2001-tractability,
    title = "Tractability and Structural Closures in Attribute Logic Type Signatures",
    author = "Penn, Gerald",
    booktitle = "Proceedings of the 39th Annual Meeting of the Association for Computational Linguistics",
    month = jul,
    year = "2001",
    address = "Toulouse, France",
    publisher = "Association for Computational Linguistics",
    url = "https://preview.aclanthology.org/jlcl-multiple-ingestion/P01-1054/",
    doi = "10.3115/1073012.1073066",
    pages = "418--425"
}