Zhu, H., F. Nan, Z. Wang, R. Nallapati, and B. Xiang. “Who Did They Respond To? Conversation Structure Modeling Using Masked Hierarchical Transformer”. Proceedings of the AAAI Conference on Artificial Intelligence, vol. 34, no. 05, Apr. 2020, pp. 9741-8, doi:10.1609/aaai.v34i05.6524.