N. Du, M. Wang, L. Tran, G. Lee, and I. Shafran. Proceedings of the 2019 Conference on Empirical Methods in Natural Language Processing and the 9th International Joint Conference on Natural Language Processing (EMNLP-IJCNLP), page 4980--4991. Hong Kong, China, Association for Computational Linguistics, (November 2019)
B. Sigurbjörnsson, and R. van Zwol. WWW '08: Proceeding of the 17th International Conference on World Wide Web, page 327--336. New York, NY, USA, ACM, (2008)