Person Cross Document Coreference with Name Perplexity Estimates Octavian Popescu author 2009-08 text Proceedings of the 2009 Conference on Empirical Methods in Natural Language Processing Philipp Koehn editor Rada Mihalcea editor Association for Computational Linguistics Singapore conference publication popescu-2009-person https://aclanthology.org/D09-1104/ 2009-08 997 1006