Ma, T., and J. Chen. “Unsupervised Learning of Graph Hierarchical Abstractions With Differentiable Coarsening and Optimal Transport”. Proceedings of the AAAI Conference on Artificial Intelligence, vol. 35, no. 10, May 2021, pp. 8856-64, https://ojs.aaai.org/index.php/AAAI/article/view/17072.