From N-Grams to Collocations: An Evaluation of Xtract Frank A Smadja author 1991-06 text 29th Annual Meeting of the Association for Computational Linguistics Association for Computational Linguistics Berkeley, California, USA conference publication smadja-1991-n 10.3115/981344.981380 https://aclanthology.org/P91-1036/ 1991-06 279 284