Head-Lexicalized Bidirectional Tree LSTMs Zhiyang Teng author Yue Zhang author 2017 text journal article Transactions of the Association for Computational Linguistics continuing MIT Press Cambridge, MA periodical academic journal teng-zhang-2017-head 10.1162/tacl_a_00053 https://aclanthology.org/Q17-1012/ 2017 5 163 177