Tractability and Structural Closures in Attribute Logic Type Signatures Gerald Penn author 2001-07 text Proceedings of the 39th Annual Meeting of the Association for Computational Linguistics Association for Computational Linguistics Toulouse, France conference publication penn-2001-tractability 10.3115/1073012.1073066 https://aclanthology.org/P01-1054/ 2001-07 418 425