Text Retrieval for Language Learners: Graded Vocabulary vs. Open Learner Model John Lee author Chak Yan Yeung author 2021-09 text Proceedings of the International Conference on Recent Advances in Natural Language Processing (RANLP 2021) Ruslan Mitkov editor Galia Angelova editor INCOMA Ltd. Held Online conference publication lee-yeung-2021-text https://aclanthology.org/2021.ranlp-1.91/ 2021-09 798 804