@InProceedings{liang-EtAl:2015:EMNLP,
  author    = {Liang, Chen  and  Wu, Zhaohui  and  Huang, Wenyi  and  Giles, C. Lee},
  title     = {Measuring Prerequisite Relations Among Concepts},
  booktitle = {Proceedings of the 2015 Conference on Empirical Methods in Natural Language Processing},
  month     = {September},
  year      = {2015},
  address   = {Lisbon, Portugal},
  publisher = {Association for Computational Linguistics},
  pages     = {1668--1674},
  url       = {https://aclweb.org/anthology/D/D15/D15-1193}
}