Empty element recovery by spinal parser operations Katsuhiko Hayashi author Masaaki Nagata author 2016-08 text Proceedings of the 54th Annual Meeting of the Association for Computational Linguistics (Volume 2: Short Papers) Katrin Erk editor Noah A Smith editor Association for Computational Linguistics Berlin, Germany conference publication hayashi-nagata-2016-empty 10.18653/v1/P16-2016 https://aclanthology.org/P16-2016/ 2016-08 95 100