Z. Yang, D. Yang, C. Dyer, X. He, A. Smola, and E. Hovy. Proceedings of the 2016 Conference of the North American Chapter of the Association for Computational Linguistics: Human Language Technologies, page 1480--1489. San Diego, California, Association for Computational Linguistics, (June 2016)
Y. Matsuo, and M. Ishizuka. Proceedings of the Sixteenth International Florida Artificial Intelligence Research Society Conference, page 392-396. AAAI Press, (2003)