X. Wang, Z. Wang, X. Han, W. Jiang, R. Han, Z. Liu, J. Li, P. Li, Y. Lin, and J. Zhou. Proceedings of the 2020 Conference on Empirical Methods in Natural Language Processing (EMNLP), page 1652--1671. Online, Association for Computational Linguistics, (November 2020)
T. Liu, J. Xu, T. Qin, W. Xiong, and H. Li. SIGIR '07: Proceedings of the Learning to Rank workshop in the 30th annual international ACM SIGIR conference on Research and development in information retrieval, (2007)