Nested Named Entity Recognition via Second-best Sequence Learning and Decoding Takashi Shibuya author Eduard Hovy author 2020 text journal article Transactions of the Association for Computational Linguistics continuing MIT Press Cambridge, MA periodical academic journal shibuya-hovy-2020-nested 10.1162/tacl_a_00334 https://aclanthology.org/2020.tacl-1.39/ 2020 8 605 620