@inproceedings{lee-yeung-2021-text,
    title = "Text Retrieval for Language Learners: Graded Vocabulary vs. Open Learner Model",
    author = "Lee, John  and
      Yeung, Chak Yan",
    editor = "Mitkov, Ruslan  and
      Angelova, Galia",
    booktitle = "Proceedings of the International Conference on Recent Advances in Natural Language Processing (RANLP 2021)",
    month = sep,
    year = "2021",
    address = "Held Online",
    publisher = "INCOMA Ltd.",
    url = "https://preview.aclanthology.org/fix-sig-urls/2021.ranlp-1.91/",
    pages = "798--804"
}